About a week ago, I experienced the exact same thing you explained in this thread. I read your post twice to make sure if it is what I experienced. In my opinion, I am really sure, it is not my computer, it is not my graphic card, it is not my RAM, because what? because before the problem started, it was all normal, I played it without any lag, any problem or any issue. My game itself have no significant changes within 2 weeks so I am also sure that it is not about Legacy family decay or whatsoever.
However my problem started after this event, one of my sim got a Hero ceremony at City Hall (SV) a lot of sims on that lot, after the ceremony, my sim went back to the house and, the problem started, it lagged a little bit, and it "paused", the plumbob, the fountain water, all animations moving, but sims all freezed about 15-20 seconds and back to normal, a minute later it happen again, and again. I quit, restart, it's all the same, clear cache and all, still not working.
But this problem fixed 24 hours later. now I can play it just like normal. no lag or stutter at all. What I did was 1 step,
[ resetSim * ]
type exactly that like you typed a cheat, without bracket, and don't change that asterisk.
Well at least in my case, it worked right away. I really hope this helps you.
[other opinion if I may add, I think this game doesn't really need Mega-monstrous RAM, yes it need RAM but 2 Gigs is enough, 16 Gigs is just ... well.. expensive? . Windows default itself only allow maximum 2 gigs of memory usage per application (task). you have to manually alter the default to make it work over 2 gigs, with my 3 gigs RAM installed, mine now at 2,5 gigs per application and it fixed the famous choppy of different kind problem that has a thread in this forum. My opinion, if you want the game to load faster, use SSD as your system disk, and even better SSD also for your sims 3 installation. Well i'm not a computer genius, I just happen to be a geek with some opinion, Thankyou =) ]