Apologies if this is how it already works, but Rimworld noticeably slows down when colonists start idling a lot and looking for jobs over and over. I suggest inverting the logic for idle pawns and having them wait a while and instead of having each idling pawn search for something to do, let them idle without doing any checks, maybe relax in chairs somewhere or just wander, do occasional single lazy checks for things like hauling and checking for the minimum necessary ingredients for any active undone bill on the map every now and then, then assigning the lazy found job to an idle pawn who reverts to normal job search behavior until they next go idle.
Once again, apologies if this is already the behavior, as I'm making an assumption that idle pawns keep looking for new jobs per pawn instead of waiting for the game to find something for them.