What Should I Do: SOLVED

I'll second @BoergeAarg61 Change your graphics settings. My old computer lagged massively and lot size had no impact, at least in my case. If my sim went to say the square in San Myshuno outside Waterside Warble things would be ok until a ton of sims started showing up. Similar thing with zooming out. If I pulled the camera back for a wider shot it would lag a bit or if I tilted it down so that it looked like I was at eye level with them. I hated to do it but I had to run the game at lower resolutions if I wanted to keep the detail level high on my sims themselves.