How to run Visual Studio 2015 and 2017 on the same machine? - visual-studio

Question

I installed Visual Studio Community 2015 on a server running Windows Server 2012 R2. I confirmed that the toolchain was able to build my C++ project (which uses CMake).
I then installed Visual Studio Community 2017 and confirmed that the toolchain was working as well. However, to my dismay, I soon discovered that the 2015 toolchain was no longer working. Trying to build my project resulted in the following errors:
-- The C compiler identification is MSVC 19.0.24215.1
-- The CXX compiler identification is MSVC 19.0.24215.1
-- Check for working C compiler: C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC/bin/cl.exe
-- Check for working C compiler: C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC/bin/cl.exe -- broken
CMake Error at C:/Program Files/CMake/share/cmake-3.8/Modules/CMakeTestCCompiler.cmake:51 (message):
The C compiler "C:/Program Files (x86)/Microsoft Visual Studio
14.0/VC/bin/cl.exe" is not able to compile a simple test program.
It fails with the following output:
Change Dir: C:/Users/Nathan/Documents/repositories/qmdnsengine/build/CMakeFiles/CMakeTmp
Run Build Command:"nmake" "/NOLOGO" "cmTC_614a9\fast"
"C:\Program Files (x86)\Microsoft Visual Studio
14.0\VC\BIN\amd64\nmake.exe" -f CMakeFiles\cmTC_614a9.dir\build.make
/nologo -L CMakeFiles\cmTC_614a9.dir\build
Building C object CMakeFiles/cmTC_614a9.dir/testCCompiler.c.obj
C:\PROGRA~2\MICROS~1.0\VC\bin\cl.exe
#C:\Users\Nathan\AppData\Local\Temp\2\nmB42E.tmp
testCCompiler.c
Linking C executable cmTC_614a9.exe
"C:\Program Files\CMake\bin\cmake.exe" -E vs_link_exe
--intdir=CMakeFiles\cmTC_614a9.dir --manifests --
C:\PROGRA~2\MICROS~1.0\VC\bin\link.exe /nologo
#CMakeFiles\cmTC_614a9.dir\objects1.rsp
#C:\Users\Nathan\AppData\Local\Temp\2\nmB577.tmp
RC Pass 1 failed to run.
NMAKE : fatal error U1077: '"C:\Program Files\CMake\bin\cmake.exe"' :
return code '0xffffffff'
Stop.
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio
14.0\VC\BIN\amd64\nmake.exe"' : return code '0x2'
Stop.
CMake will not be able to correctly generate this project.
Call Stack (most recent call first):
CMakeLists.txt:2 (project)
-- Configuring incomplete, errors occurred!
See also "C:/Users/Nathan/Documents/repositories/qmdnsengine/build/CMakeFiles/CMakeOutput.log".
See also "C:/Users/Nathan/Documents/repositories/qmdnsengine/build
What does this error mean and how would I go about fixing it?