Soph was in a cast when she was a pup and was in it for 8 weeks. Dogs heal quickly but 15 days seems way too soon to have removed the cast in my opinion. I'd say a trip back to your vet is definitely in order.
Also something to keep in mind down the road....once Soph's cast came off, bone healed completely, absolutely 110% on the leg......for about a month after any time she saw us watching her run around she'd immediately slow to a walk and start limping
, looking over her shoulder at us to make sure we were seeing what a poor injured little creature she was. Of course when she didn't know we were watching she would run around like a nut, no limp whatsoever