youre map has got potential.. it doesnt lagg at all on my comp, and mine is really old crappy ibm.. maybe you need to manually delete the history, temp, temporary internet files, and defrag.??
oh! and you need to add a step in the tunnel! once you get down there youre stuck to be shot at.. all jumpable items have to be 1/3 or less height to be able to get on them without low gravity.. just a little pointer.