Hey,
I have experienced the same problem as you, but mine is not as bad. Mostly during create a sim, the game freezes for about 30 seconds and then carries on as before. This is extremely annoying, because it causes the sims to become deformed after it has loaded them again.
I suggest that you put your graphics options on minimum ( Can be found in options under the graphics tab). Although your sims might look bad, it speeds the game up as it doesn't have to cope with loading high quality images.
It could also be the amount of content you have in your game. For example, having a lot of sims 3 store content, or having a lot of expansion packs on your game. Although there is nothing you can really do about this, I suggest choosing your favourite expansion / stuff packs and uninstalling the rest.
Also I advise uninstalling and 3rd party mods not licences by EA. They may claim to help your game and improve the running of it, sometimes it mucks it up even more. The only Patches you should have on your game are the ones licences by Ea, however fun and intresting other mods should be.
Also, check that your computer meets the minimum requirements of the game. There are lots of issues with graphics and freezing, due to the graphics cards compatible with your computer and game. If possible update your Graphics card.
Hope this helps,
Superflatface.