I've had the refresh time get up much higher than 150. It's also easy to reproduce as well. I had it at 180. When the camera is close to something, it really hurts this, don't know why. I was right next to a large chunk of intersecting, criss-crossing blocks off fairly odd sizes (96x96 block size using a 16x16 texture). I could sort of replicate this and make it more severe (like 400). It might be a bug in the engine (since 6.22), but can't say for sure.