Short answer is no, do not just run fast vis, that is good for checking lighting only.

Fast Vis= basic vis calculating loaded from .prt file, will result in finished lighting but a very poorly optimized map. If your compile is choking, it's likely that it's stuck on the PortalFlow process of Normal vis, which means you have some work to do. Normally this means that you have too many little brushes set to world and not func_detail.

It all boils down to reading and understanding this:

http://www.student.ru.nl/rvanhoorn/optimization.php