i am not sure how the level was created but from what i see this is way below what 3dgs can. either there is some code issue or the level is made out of level blocks and without lod.

gs is a bsp engine and outdoor levels need to be treated very special or they wont work.

as a side note i must say that i am disapointed about how the level looks like.
all the fuzz for a plane ground with very bad textured houses?!


this old level i made runs without much optimizations and with some old techniques i used with about 70fps:


a level i am working on right now uses 4 times the quality, more optimizations and consequent lod systems and runs with solid 50 fps.

so i am not sure where your cpu power has gone.
there must be an issue with the level

cheers and keep it up