I was noticing that (big surprise) sims load faster with the sim browser if you only open the category that you are editing. Unfortunately if you are opening a townie for any reason, you cannot currently remove the playable sims from the list.

It would also be nice if the list would let you filter townies from Downtownies, University townies, etc, but that would be even less necesssary and probably even more work for you, so I'm only requesting it if you have already thought of a way to filter the NPCs by thier respective families rather than just sorting them later.

(Of course that would probably lead to wanting to filter the Playable sims by family as well.)