Considering how little it can do for someone OLDER WITH DECLINING HORMONE LEVELS, id say for a 15 year old its about as useful as a blow up doll with no holes
if you have trouble gaining mass at your age perhaps looking over other areas, diet, training are in order.
my younger brother is 19, and barely lifts regularly and got a decent amount mass on him in short bouts of lifting. i cant image what the young kids can do with serious training man. maybe a carbohydrate disposal agent would benefit you, anabolic pump, something in aid of a good diet would be BEST for you IMO. at your age your hormones near peak levels, what some people using this products may not even get to with lol.