The 15 series was the model with adjustable sights, the -2 originally referred to the barrel length. 15-2, 15-4, 15-6, 15-8, ect,,, The stainless models had a 7 before the 15 as 712, 714, 715. You can get a barrel wrench for it and get additional barrels from 2" to 15" The 12" and 15" are no longer produced but come up on auction sites regularly. I had a Monson 15 for years and it was the most accurate pistol I had. The trigger was a little stiff. If yours is; they have spring kits which are easy to replace, thanks to the side plate design. I put a Bullseye kit and single action was almost dangerous, very light. The only drawback was it wouldn't fire some factory ammo due to light strike. I used WW primers and reloaded with 100% firing. Many parts from the new DW's fit the older models; barrels, shrouds hammers ect..There are also a lot of new old stock parts out there in old gun shops and come up on auction regularly.