I've been experiencing extremely low FPS in Minecraft Snapshots for 1.9, just recently 15w31c. The frame rate doesn't go above 40 and it doesn't matter if I'm in an empty world or in a world filled with blocks and hugs - I tried to set my render distance down from 12 to 2 chunks, still had around 40 fps. In Minecraft 1.8 to 1.8.8 running without mods I had around 90-100 fps almost at all times. Running in fullscreen did not solve the problem. See the attached picture for more information.