Very rare(but exist :P) - I've done the same but I was on lol - but after that cycle - I've actually grown more(bf about the same if not a tad higher) but I gained 20+lbs and dropped about 4% bf) it's doable but rare - especially as dj stated 15kg = 33lbs that's a lot w/out help - or he knows how to eat and grow at 15-16(another rarity)