Is the game using your dedicated graphics card? Go into Documents > Electronic Arts > The Sims 3, open deviceconfig.log, and look for your GPU name about 30 lines down. If it's showing the Intel chip, you can tell Windows to use the Nvidia card for Sims 3 instead. Hit Windows key-i, select System > Display > Graphics settings, click Browse, select TS3.exe (Origin install) or TS3W.exe (with the W, disc Steam install), click Options, choose the "High performance" option, and save.
Regardless of whether you have to change the Windows setting, please post the two lines in deviceconfig under "Rating info," which should be in this format:
GPU: 5 GPU Memory: 4 CPU: 2 RAM: 4 CPU Speed: 2900 Threading: 2
Adjusted CPU: 2500 RAM: 15791 Adjusted RAM: 15279 Cores: 1