Archangel said:Maybe 3? And that's only if they're the 3/4" kind you can find around here. And when they are young, they are not slow growers. 2 of mine have grown from 2 inches to 4 1/2 in just 4 months. I wouldn't leave them in the 15 after they reached an inch and a half. I really wouldn't recommend even trying to grow them out in a 15. The larger the tank the faster they'll grow. But you'll do what you want to do.