I don't know why, I really like that map, for some reason, good atmosphere...
May I ask what your average r_speeds are? I think you can spare some polys though...and I also see what CS means with the dirt and rocky texture, but I don't really think it's that bad.
that water looks nice, but maybe increase the size of it to make less lag or just use 2 func_conveyors and make that texture scrollyourwatername then just make each on flow in different directions then make a third brush that goes right over em, tie it to the entity func_water and then make the texture just null and if youy want make tex. size 100. that causes no fps loss at all according to my knowledge.