Well, you've got me baffled. What would be the difference between a 4" Model 14 and a Model 15?
I'm not so much on this new Model numbering system, I knew them as the K-38 Masterpiece (6") and the K-38 Combat Masterpiece (4"), then came the Combat Magnum (Model 19) and Distinguished Combat Magnum (Model 586).
Could your gun have been rebarreled?
Bob Wright
P.S. Whatever it is, you've got a great old revolver!