I don't know much about limit of saves, I have played personal dynasties up to five generations, with in some eight sims in the house at the same time. Once a family was established I never had below six in the house after the first generations. I was at save 10.? when I had to uninstall a lot of games, around three families in each town, the smallest was at third generation with a save at 5. ?
Mansions were three stories, six or more bedrooms with own bathrooms plus two master bedrooms with double bathrooms, two nurseries, one downstairs and one on second floor. Extra full bathroom on each floor, alchemy room, exercise room, martial art room, formal living room, family room, formal dinning room, family dining area, library/study (good size, five desks for computers, five or more bookshelves, chairs and other items) small rec area, indoor pool, at least five fireplaces, grill area outside, playground outside, good size pond with quiet area to sit and relax, three car garage. This was with most of my families so I am figuring that it would have taken up a lot of space.
Along with several single families, created four gardens to use in town games, and several single sims in towns to use as mates if needed.
I had probably three times more than what I have now and I was starting to have problems and later realized it was connected to something other than the sim games.
And my computer is four or five years old.
That is why I can't see that as the problem, my largest families are at three generations and I have only two of them, the rest are single or second generations, around five of them; not counting my three project families, with each at the second generation and in much smaller homes. I have 10 families that have three kids in each family. They are seed families.