If I play a massive house on a massive (for me community) lot I have issues also. Not quite as bad as that but bad enough for me to not play it that way. I'm not talking size massive. It has to do for me with how many objects are there. So if it's a multistory building basically taking up a huge lot with multiple objects on it like fountains ect. I have noticeable lag. To put in in some perspective though none of the Maxis made big community lots give me lag like that. Nor the bigger houses for that matter.
It is too much for either of your systems I'm betting. Go to a smaller lot and see if there is a difference. If you still have the pausing issue then maybe it's something else.
