Extension Won't Debug - debugging

Question

I have a VSIX package in a 2015 Solution, targetting VS2013. Whenever I try to run it against the VS2013 Experimental Instance, the extension doesn't show up in the installed list.
However, I am able to manually install the .vsix file into 2013 by double clicking on it. This will install (and run) successfully.
The settings for creating the .vsix and deploying it to Exp appear to be correct. What am I missing?
Manifest
<?xml version="1.0" encoding="utf-8"?>
<PackageManifest Version="2.0.0" xmlns="http://schemas.microsoft.com/developer/vsx-schema/2011" xmlns:d="http://schemas.microsoft.com/developer/vsx-schema-design/2011">
<Metadata>
<Identity Id="9D7E0DF5-0A4D-4B43-9D73-4AD3F83260FA" Version="1.2" Language="en-US" Publisher="VersionOne" />
<DisplayName>VersionOne TFS Checkin Policy</DisplayName>
<Description xml:space="preserve">TFS Checkin policy from VersionOne for Visual Studio 2013. Requires code commits to contain a VersionOne identifier</Description>
<License>LICENSE.md</License>
<Icon>logo.ico</Icon>
</Metadata>
<Installation>
<InstallationTarget Id="Microsoft.VisualStudio.Pro" Version="[12.0]" />
<InstallationTarget Version="[12.0]" Id="Microsoft.VisualStudio.Premium" />
<InstallationTarget Version="[12.0]" Id="Microsoft.VisualStudio.Ultimate" />
</Installation>
<Dependencies>
<Dependency Id="Microsoft.Framework.NDP" DisplayName="Microsoft .NET Framework" d:Source="Manual" Version="[4.5]" />
</Dependencies>
<Assets>
<Asset Type="Microsoft.VisualStudio.VsPackage" d:Source="File" Path="RegistryKeyToAdd.pkgdef" />
</Assets>
</PackageManifest>
Project File
<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<MinimumVisualStudioVersion>14.0</MinimumVisualStudioVersion>
<VisualStudioVersion Condition="'$(VisualStudioVersion)' == ''">11.0</VisualStudioVersion>
<VSToolsPath Condition="'$(VSToolsPath)' == ''">$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)</VSToolsPath>
<FileUpgradeFlags>
</FileUpgradeFlags>
<OldToolsVersion>12.0</OldToolsVersion>
<UpgradeBackupLocation>
</UpgradeBackupLocation>
<PublishUrl>publish\</PublishUrl>
<Install>true</Install>
<InstallFrom>Disk</InstallFrom>
<UpdateEnabled>false</UpdateEnabled>
<UpdateMode>Foreground</UpdateMode>
<UpdateInterval>7</UpdateInterval>
<UpdateIntervalUnits>Days</UpdateIntervalUnits>
<UpdatePeriodically>false</UpdatePeriodically>
<UpdateRequired>false</UpdateRequired>
<MapFileExtensions>true</MapFileExtensions>
<ApplicationRevision>0</ApplicationRevision>
<ApplicationVersion>1.0.0.%2a</ApplicationVersion>
<IsWebBootstrapper>false</IsWebBootstrapper>
<UseApplicationTrust>false</UseApplicationTrust>
<BootstrapperEnabled>true</BootstrapperEnabled>
<TargetFrameworkProfile />
</PropertyGroup>
<Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
<PropertyGroup>
<Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
<Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
<SchemaVersion>2.0</SchemaVersion>
<ProjectTypeGuids>{82b43b9b-a64c-4715-b499-d71e9ca2bd60};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
<ProjectGuid>{2153C73F-1BA9-49F8-BAB2-84F7769BD67A}</ProjectGuid>
<OutputType>Library</OutputType>
<AppDesignerFolder>Properties</AppDesignerFolder>
<RootNamespace>VersionOne.Integration.Tfs.Policy.Deployment.VS2013</RootNamespace>
<AssemblyName>VersionOne.Integration.Tfs.Policy.VS2013</AssemblyName>
<TargetFrameworkVersion>v4.5.1</TargetFrameworkVersion>
<GeneratePkgDefFile>false</GeneratePkgDefFile>
<IncludeAssemblyInVSIXContainer>false</IncludeAssemblyInVSIXContainer>
<IncludeDebugSymbolsInVSIXContainer>false</IncludeDebugSymbolsInVSIXContainer>
<IncludeDebugSymbolsInLocalVSIXDeployment>false</IncludeDebugSymbolsInLocalVSIXDeployment>
<CopyBuildOutputToOutputDirectory>false</CopyBuildOutputToOutputDirectory>
<CopyOutputSymbolsToOutputDirectory>false</CopyOutputSymbolsToOutputDirectory>
</PropertyGroup>
<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
<DebugSymbols>true</DebugSymbols>
<DebugType>full</DebugType>
<Optimize>false</Optimize>
<OutputPath>bin\Debug\</OutputPath>
<DefineConstants>DEBUG;TRACE</DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
<CreateVsixContainer>True</CreateVsixContainer>
<DeployExtension>True</DeployExtension>
</PropertyGroup>
<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
<DebugType>pdbonly</DebugType>
<Optimize>true</Optimize>
<OutputPath>bin\Release\</OutputPath>
<DefineConstants>TRACE</DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
</PropertyGroup>
<ItemGroup>
<Compile Include="Properties\AssemblyInfo.cs" />
</ItemGroup>
<ItemGroup>
<Content Include="..\VersionOne.Integration.Tfs.Policy.Deployment.Shared\logo.ico">
<Link>logo.ico</Link>
<IncludeInVSIX>true</IncludeInVSIX>
</Content>
<Content Include="..\VersionOne.Integration.Tfs.Policy.Deployment.Shared\RegistryKeyToAdd.pkgdef">
<Link>RegistryKeyToAdd.pkgdef</Link>
<CopyToOutputDirectory>Always</CopyToOutputDirectory>
<IncludeInVSIX>true</IncludeInVSIX>
</Content>
<Content Include="..\VersionOne.Integration.Tfs.Policy.Deployment.Shared\LICENSE.md">
<Link>LICENSE.md</Link>
<CopyToOutputDirectory>Always</CopyToOutputDirectory>
<IncludeInVSIX>true</IncludeInVSIX>
</Content>
<None Include="app.config" />
<None Include="source.extension.vsixmanifest">
<SubType>Designer</SubType>
</None>
</ItemGroup>
<ItemGroup>
<BootstrapperPackage Include=".NETFramework,Version=v4.5">
<Visible>False</Visible>
<ProductName>Microsoft .NET Framework 4.5 %28x86 and x64%29</ProductName>
<Install>true</Install>
</BootstrapperPackage>
<BootstrapperPackage Include="Microsoft.Net.Client.3.5">
<Visible>False</Visible>
<ProductName>.NET Framework 3.5 SP1 Client Profile</ProductName>
<Install>false</Install>
</BootstrapperPackage>
<BootstrapperPackage Include="Microsoft.Net.Framework.3.5.SP1">
<Visible>False</Visible>
<ProductName>.NET Framework 3.5 SP1</ProductName>
<Install>false</Install>
</BootstrapperPackage>
</ItemGroup>
<ItemGroup>
<ProjectReference Include="..\VersionOne.Integration.Tfs.Policy.VS2013\VersionOne.Integration.Tfs.Policy.VS2013.csproj">
<Project>{24b4af99-795b-4b33-ad1d-fd51f32e2aeb}</Project>
<Name>VersionOne.Integration.Tfs.Policy.VS2013</Name>
</ProjectReference>
</ItemGroup>
<Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
<Import Project="$(VSToolsPath)\VSSDK\Microsoft.VsSDK.targets" Condition="'$(VSToolsPath)' != ''" />
<!-- To modify your build process, add your task inside one of the targets below and uncomment it.
Other similar extension points exist, see Microsoft.Common.targets.
<Target Name="BeforeBuild">
</Target>
<Target Name="AfterBuild">
</Target>
-->
</Project>

Answer 1

You need to configure your project to deploy to VS2013, even when run from VS2015.
Sam Harwell wrote a NuGet package that does exactly that; just install that package and you should be good to go.