Depending on your age, sex and genetic factors it may be impossible to gain 10-15 pounds of lean muscle mass. Drugs, of course could aid any dedicated training program.

It is possible, that you will gain 10-15 pounds at some point if you attempt heavy training. But understand that much the weight is actually fluids and non-muscle materials associated with blood vessels.

Often people will develop larger body parts, or limbs, without significantly increasing muscle. That's why cycling doesn't work for many womens' butts........ but I digress......