I have the exact same problem. Ran 1.5.2 with the old launcher at 60-150FPS (On highest settings), now I'm down to 10-25 (On lowest settings.) Dinnerbone said to switch to dedicated graphics; however, the majority of laptops only have integrated. Surely the game hasn't changed so much that it's no longer playable for many of us? Thank you kindly.
I think it's a bit surprising. Mojang has a reputation for fantastic customer service. But, much like other people, the only answer to this large problem is "use dedicated graphics." Which, for many of us with laptops, may as well be "get a new computer." I don't see how it isn't fixable. The only change to the game was adding horses and a few blocks. How does that cause a 90% FPS decrease? I hope it does get fixed soon.