You did try playing in a lower resolution, or with reduced graphical settings?
Especially a setting like high detail lots can be disastrous to your gameplay. Leave it at 1.
my game actually doesn't "lag", it just freezes (but the ZzzZZ coming from my sim sleeping is still going if u know wat i mean) like how it feezes at 1 after 3-4 in game minutes. i always have to save quit or main menu and save but sometimes when i go back in a few seconds later i get crash out onto desktop