First of all make sure you have the game located in your SSD that helps a lot, now commonly the game performance problem is due to the characters, the more characters you have in your game you will have more lag, also keep in mind the amount of mods and accessories that the characters you use have, you can have a few characters in your game, like 5 or 6 simultaneously, but if those 5 or 6 have a lot mods and accessories that will also affect the performance.