DWalt has answered the question very well. In my opinion, all years that the Model 15 was produced are rather exceptional. They have been the best holster sidearm in .38 special ever produced. The craftsmanship is evident in all years of production. I have a a 1950 production example up to the 15-7 Heavy barrel 4". I have found the model to be consistent in workmanship and fit in the 10 I own, which cover most years of production.
I believe that Smith and Wesson hit the proverbial home run with this model as far as a perfect example of an all purpose .38 special caliber revolver that can do most things that the average owner, be he/she a civilian, Police Officer, Security Officer or anyone who needs or wants to have a sidearm that is easy to use and carry.