That does look pretty cool; although, some of the walls look flat and uninteresting. He could probably put some trim around the windows and on top of the walls to help make that better. However, then we get back to r_speeds.
He may want to consider using a lower-res mesh for the rocks to lower the r_speeds. If it was for Q2, he could try making a bunch of the brushes used for detailing into detail brushes. But since it's for Q1, he could make those detailing brushes into func_walls. There's a great article over on Rust that offers many tips for reducing r_speeds in Q2, so maybe he should check that out; there might be some relevant stuff.
http://www.gamedesign.net/?file=rust/content/quake2/tutorials/poly_count
But then again, your brother may already know all this stuff.