Dang...15 years old!?!??!! He's barely just hit puberty.
Criminy; I'd say lay off this shit until you're at least in your late 20s. Man, I gained 60 lbs as an ectomorph between the ages of 24 and 27, so the natural hormones are there to do it. Yeah, boo hoo, it was real hard and I had to eat like a maniac. Food ruled my life more than a bulemic.
But, I knew I was big when I backed into this dude's car and he was coming up to the side and I got out and he turned around and walked away. And, I even gave him shit "don't park your fuckin car so far forward." That was worth the effort right there. I cannot imagine that juicing before you've even hit your full height can be anything but HUGELY detrimental.