Unless you are one who likes to "scrunch" up on a stock, at 6' tall, 15 is not necessarily too long. A lot of things determine LOP, grip style being one of the major reasons.
Pick a spot on the wall, close your eyes, raise your UNloaded gun to your shoulder and open your eyes - are they locked on that point on the wall and not seeing any rib? Then your fit is close. However, drop at heel, drop at comb, cast, pitch, thickness of the comb, etc. are also factors affecting fit besides LOP