At lot of this is the problem with computers now then just an individual engine.

A big thing you can do is to group as many models as you can into one model. This will help you a lot.

Next try to limit how far the camera can see. If you want to know what i mean point the camera at a wall and then point it at an open field with many models in it. You'll see a huge difference.

Limit your traces. If using it for AI for several entites don't do it every frame, use it once a second. This should help a lot.

Stay away from anything in the manual that is labled "slow". Or do your best not to. Try to use 3dgs functions instead of scripting your own. C++ is faster then C-script so it's better to use theirs.

Pray to Foxhound daily, this helps the most.