[Help] Map/Game Optimization ?

Hello !
I would like to know if anyone has some tips about map optimization ?
I'm PvPing with friends on a very small map and theyre getting bad FPS...
Maybe there are some basics things to do with the editor to fix this ? This is the first map I made from scratch :/
There is no grass, but a lot of small objects. There is no post FX or color correction.

We're also all getting a lot of crashes "out of memory", when we've got beast computers :( And longer we stay without going back to the menu, worse are the FPS. The memory must be leaking like crazy, but I don't know if this problem comes from the map.

Here's a video of the map, if it can helps :
https://www.youtube.com/watch?v=BfflqH1Tc80

Thanks !

Edit :
Oh and I'm running the server on a VM, and the client on the same computer (and Fraps, Teamspeak, Youtube as well :p). I don't think the problem comes from there but who knows.