Laravel 7 queued email very slow with attachment but fast without - laravel

Question

I use Laravel 7 queues / jobs to send a newsletter to multiple addresses and it works well and rather fast. But when I send a single email with attachment (22ko PDF), it takes nearly 3 - 5 minutes to get through. Any clues? I use database driver and Mailgun API.
How can I see if the slow process time is from Laravel app or Mailgun or else?
I tried to use SendEmailJob::dispatchNow($data); but it does not speed up the process.
app\Http\controllers/EmailController.php
App\EmailController
use App\Job\SendEmailJob;
public function send()
{
$data = array(
'from_name'=>from_name',
'from_email'=>'admin#domain.com',
'to_name'=>$user->firstname." ".$user->name,
'to_email'=>$user->email,
'subject'=>'This is test email',
'reply_to'=>noreply#domain.com,
'model'=>$invoice,
'locale'=>app()->getLocale(),
'user'=>$user,
'view'=>'emails.invoice',
'filefullpath'=>$fullfilepath,
);
SendEmailJob::dispatch($data);
}
App\Jobs\SendEmailJob.php
namespace App\Jobs;
use Illuminate\Bus\Queueable;
use Illuminate\Queue\SerializesModels;
use Illuminate\Queue\InteractsWithQueue;
use Illuminate\Contracts\Queue\ShouldQueue;
use Illuminate\Foundation\Bus\Dispatchable;
use App\Mail\SendView;
use Mail;
class SendEmailJob implements ShouldQueue
{
use Dispatchable, InteractsWithQueue, Queueable, SerializesModels;
protected $data;
/**
* Create a new job instance.
*
* #return void
*/
public function __construct($data)
{
$this->data = $data;
}
/**
* Execute the job.
*
* #return void
*/
public function handle()
{
$email = new SendView($this->data);
$email->replyTo($this->data['reply_to']);
$email->subject($this->data['subject']);
if(isset($this->data['filefullpath']))
{
$email->attach($this->data['filefullpath']);
}
Mail::to($this->data['to_email'], $this->data['to_name'])->send($email);
}
}
App\Mail\SendView.php
<?php
namespace App\Mail;
use Illuminate\Bus\Queueable;
use Illuminate\Contracts\Queue\ShouldQueue;
use Illuminate\Mail\Mailable;
use Illuminate\Queue\SerializesModels;
class SendView extends Mailable
{
use Queueable, SerializesModels;
protected $data;
/**
* Create a new message instance.
*
* #return void
*/
public function __construct($data)
{
$this->data = $data;
}
/**
* Build the message.
*
* #return $this
*/
public function build()
{
$view = $this->data['view'];
$user = $this->data['user'];
$model = $this->data['model'];
$locale = $this->data['locale'];
$array = $this->data['array'];
return $this->view($view, compact('user', 'model','locale','array'));
}
}
Please help! Thanks.