Anyone who may be having game performance issues, with Sims 4 may want to try a game booster. I recommend Razer cortex: boost
What Razer Cortex Boost Does:
Optimizes Your PC for Gaming
100% FREE, just have to create an account
Made for All PCs
Defrags Your Game Folder for Quicker Loading
Backup saved games & Access Your Save Game Files from Anywhere
http://www.razerzone.com/cortex/boost
Razer's GameBooster should automatically close everything (that isn't a system process) when you open a specified program such as a game, and then reopen it all once you're finished.
If the problem ultimately stems back to an underpowered computer, though, then there isn't really anything you can do other than upgrade your hardware. No amount of coercing will make the game run better if the hardware itself physically can not handle the game.