Minecraft uses all my CPU on snapshots

Lastest snapshots are using all my CPU and everything is slow.
For example, water will update slowly, taking like 20s to spread completely.
Slimes will take like 10s to jump and hit the ground again.

In the attachments you can see in the 1st image you can see the normal/1.7.4 CPU usage, and in the second image you can see the snapshot CPU usage.