|Have you installed any custom content? Not by way of the launcher, but .package files? If so, you may want to check to see if any of those are Sims 2 packages. That can slow the game down a LOT.|
You can check it two ways: One, just go into the folder where you installed the packages, and sort them by date. Any files showing up before say, May of last year (prior to the Sims 3 release) are more than likely Sims 2 packages. Delete them or put them to the side.
Or you can try the Sims3 Dashboard. It can filter out the Sims 2 packages, plus any corrupt files you may have.