Hmm that sounds like something is terribly wrong. My PC is not a dedicated gaming rig, at all, and even after I just re-installed the base and ALL EP's (new for me, I only had like 4 or 5 before) my game runs pretty well. I also have over 5gb of .package files, and I dont know how much sims3pack files. I run an HQ mod on HIGH sim, and high details. There is a small amount of lag when I first open (rendering the CC laden house) but definitely not when I use the camera, its slightly choppy running it at 3. I don't have lot detail on high though, that might be on med as well as some others.
I would either go here into the tech forum, or if you use NRAAs mods try over there.
You should be able to run this game well, it might just need some tinkering.