You could go old school and instead of purchasing a brand new hard drive, go for either additional ram or an external 32/64gb ramdisk.
With additional software. temp load the entire game [32gb] [and other games that you play] onto ramdisk and the speed/loadtimes/fps[to lesser extent] will be awesim.
Playing the sims using ramdisk should fix the problem, if not then its most defiantly the game, but in other ways it will benefit when playing other games.
Using ramcache it does make a difference, especially older computers.
Here a link with further info- https://rog.asus.com/technology/republic-of-gamers-motherboard-innovations/ramdisk/