Does anyone here experience low performance when you never used to?

My computer ran the game and all expansion packs just fine until Pets came out.

Now it runs like crap.

Pets was my last expansion. My computer doesn't meet the requirements, so once Late Night gave the big shells of buildings, my computer suddenly experienced a huge dip in performance. I tried playing in other towns, but once pets came out... it was just shit, really hard to deal with.