I'm thinking it probably won't. The 15 cylinder is shorter than the 19, and the part of the 19 barrel that's inside the cylinder widow (the forcing cone) is shorter. Unless you plan on adding a 19 cylinder, too.....
...or maybe you plan on having the shoulder of the barrel turned down to extend the threaded portion of the barrel.
All in all, a nice idea, but you'd be getting into some expensive territory.