Going from something like 30fps to 60fps, interpolation works decently well in many cases, because there's already so much information encoded in the 30fps. And some 15fps can work too.
But with 5fps, each frame can be so radically different, I think interpolation is generally just not possible. You can generate something smooth, but it will be so far away from whatever an animator would actually have inserted, that it will seem more strange/surreal than natural, and thus achieve the opposite effect as intended.
E.g. see [1] which shows animation at 15/30/60fps... you can see that even with the 15, it's hard to imagine an algorithm that would port well to 60. (Use the period on your keyboard to advance frame-by-frame.)