Horrible performance issues in 14w28b

In last week's snapshot, I used to play at around 65-70 FPS, and now, it's at 20-25 FPS. The same thing is happening to my friend, who used to play at 30-40 FPS and now plays at 10-15 FPS.

I know it's not an AMD or Nvidia issue, as I have an AMD GPU and he has an Nvidia.

And yes, we tried turning off Block Alternatives.