Hmm.
First off, you should, (as people were saying), Enclose this building.... thing. This will seriously improve framerates. A matter of fact, DONT even use a skybox for multiplayer. (helps a ton.)
Second, use lights, all static, and put ambiance to zero. Add light sources too.
Third, be wary of using a bunch of entities like that. Its better to just have a large map of segments. Especially if you really do have 150 people playing that! Lol.
Fourth, to add, dont lie.
Fifth, get rid of all those useless segments (doors in the middle of nowhere)
sixth, read the forum rules....
I'm a Twisted Fire Starter...