Send our own Bobby Tomek a PM and ask him. I don't know about 15" barrels but I'm pretty sure he could help you with the cartridge and its performance on deer-like critters from a carbine length barrel.

“My horn is full and my pouch is stocked with ball and patch. There is a new, sharp flint in my lock and my rifle and I are ready. It is sighted true and my eyes can still aim.”
Kaywoodie