Closing Cubase Delay

Cubase takes upwards of 2 minutes sometimes to close itself sometimes (if the project is especially large), so I just crash it via Task Manager. Is this wrong to do? I figure I might end up with a lot of temp folder files left over from the times Cubase is closed this way(?) Could these files start piling up and wasting space on C: ?

That’s not the worst thing, Cubase saves the preferences when shutting down. If you force quit it, you will end up with corrupt settings it’s just a matter of time.
You can go to the Profile Manager and save/export your settings to a safe place, when it happens you have something to get you back.

How long does it take to close the same project from the file menu/close command without actually closing Cubase?

The session closes fairly quickly but Cubase itself will hang, no matter how much you click the X in the top right corner.