Welcome to the forum bud,
First rep so you probably dont know how much of a crapshoot the movements are sometimes. I'd be happy with 15 s/d fast to be honest, as I rotate my watches more frequently.
If it really bugs you, you can open the watch up and adjust the screw or lever to the " - " side a couple of notches and you should be within 6 or 7 s/d.