how many polys, character-entities in one place, physics ... overfilling the map with ignoring your hardware-abilities is also a good cause for laggs in testgames, i think
other thing is the shaders: if you got water in your levels, it eats lots of performance in combination with characters/complex meshes, also using too much/wrong shaders on segments or entities.
other thing2:
could be that somebody says:"oh no, not again", but try this:
run fpsc cleaner, make savety-copies of the segments-fps you use in your level, then set visoverlay=0 to 1 in all fps-data used, and test it. helps me in big outdoor areals that crashed before doing this and now running on 60fps. mainly walls and floors wich are set visoverlay=0.
if any questions:
http://forum.thegamecreators.com/?m=forum_view&t=186092&b=21
p.s.: as said in the thread, to edit the map again set visoverlay into vanilla conditions again (recopy savety-copies).
