In this case by a large map file I mean a file with many templates (56) that have a number (around 10) meshes on them that define internal and external walls - the level IS horribly laggy if the camera is pointing at the templates (they are positioned in a straight line).
My guess is that CS calculates visibility based on which way the camera is pointing (it doesnt take solid walls as a factor for line of sight) since if I turn around the FPS return to normal values. So will setting the camera in an isometric perspective or so help reduce the lag or should I just reduce the number of templates because CS cant handle it?
Can anything else be done for lag reduction?
By the way I am having trouble compiling my CEL applications due to some stupid error (this is relevant since CEL makes camera work easy), I have posted about it the CEL subforum.
You could attempt to use the Dynavis visibility culler but I guess that you are using lightmapped things? These can cause a lot of performance overhead because they use a lot of texture memory. Perhaps reducing texture size or going from 16x16 to 32x32 lightmap lumel size (lightmapcellsize in settings) will help.