Updating Unity caused significant performance loss in Physics

I updated from 5.02 to 5.23, now my game lags terribly. The profiler shows the vast majority of the CPU usage coming from Physics colliders. I have 2D box or polygon colliders on about 25 game objects. It worked fine before. How has Unity changed? What do I need to do to fix this?

Nothing that I know of. Care to submit a bug report with an example case (please provide the case number) so it can be investigated?