I just loaded the preview, appeared in Lusk... and found that my framerate is about 0.5 FPS. Never remember it being so bad.
After lots of fiddling I finally figured it out: It's my head!
A couple days ago I got rather bored, took my head, and put a script in each strand of hair that makes it change color randomly. My plan was to eventually make it controllable, so that I can recolor my hair at will. On the main grid that results in increased bandwidth usage, but I didn't notice any more serious consequence.
However, in the preview, this kills framerate in a really incredible way. It can bring it down from 20 to 0.5.
If any Lindens are interested, IM me, and I'll send you the very simple script.