Anti-Virus programs can probably interfere with some processes of running games and sims.
Their task is usually, to check various processes and files for possible threats.
Now a game or sim would load files and start processes here and there, and this may activate
the Anti-Virus program in a way, that the game is getting slowed down, or even crashes.

You could switch the AV program off completely, but there you needed to make sure

- that you unplug your internet connection
- that you re-activate the AV after playing, and before you go into the internet

That's why most modern Anti-Virus programs have "Gaming Settings".
In my KASPERSKI they look like this (in German of course; I hope I translated all right):

GAMING PROFILE

- Use gaming profile

- Choose threat defense action automatically

- Don't update (during games)

- Do not launch investigation tasks (during games)

- Stop manually launched investigation tasks

All these points are ticked in my case, and I must say, I never had any problems with OFF
or other sims and games.
Just see through your AV's menue, find "Gaming Settings" (or similarly named),
and see, if there are similar tick boxes.
The AV will follow your settings ONLY while you play a game or a sim.
The AV can recognise that, as long as you play it in full screen mode (as you normally would).


Since I am far from being an expert on computer stuff, I invite everyone with valuable or
better info, to add his knowledge and experiences to this thread.