Major update caused my main world to run slow.

Since 1.2.0 came out, I loaded up my world and it was constantly laggy that it gave me a headache. I do not have many mobs, and switching to Peaceful mode does not help at all. I don't have that much redstone and they're shut off. Quitting and then rejoining does not help that much now, but before it did. Turning on Plutonium mode does not work. Versions before 1.2.0, my world was absolutely fine, well had few minor lag sometimes but that did not hurt me at all. Currently my world size is 111MB, and it was like that before 1.2.0, and had no issues. I would absolutely beg for performance to be improved for the next patch update (hopefully 1.2.3), please.