I find 10-15 minutes more practical. AutoSaving every 3 minutes will certainly slow you down too much, especially when you go into larger models.
15min is about the maximum before you get into a problem of if the program does crash, how much work needs to be re-done. Redoing 30min of work can be crushing (from personal experience). 15min of work is more annoying.
I would not revert entirely to auto save. That's bound to fail. Just remember to manually save every once in a while, especially after a major milestone in your model, because you also can't entirely rely on autosaves either.