So, I decided to open this map up in Hammer to see how you did a few things, and I noticed that the entire main portion of the map is made of pure displacements inside a giant skybox box. I suggest you put some nodraw brushes underneath the displacements and avoid making giant skybox boxes encompassing the whole map. With the strategic use of hills and various other buildings, you'd be able to greatly increase performance on this map for very little effort.