I have a Monson era Pistol Pac.
It is a great gun. Mine is Model 15-2.
In the Dan Wesson Revolver world there is not much talk about dates and serial numbers, because there are no real differences from year to year within a manufacturing era. Take a look at the Wikipedia article on the company, which is pretty good, for all I know, to understand the eras and the models that were produced.
If you have an actual Model 15 instead of a Model 15-2 that tells you that you are in the mid or early 70's.
The 6" .357 magnum was used in a shoulder holster either for duty or handgun hunting which was a fad back then. The adjustable sight is supposed to be wobbly BTW. Mine with the 8" bbl was carried in a Bianchi X-15. Where this gun really shined forth was at long range steel silhouette matches. I never competed, but the DW guns took the top honors because they could use hotter loads.
The 4" Model 14" was for Patrol, because your side arm bumps into the car seat while driving. 4 inches is perfect for that.
The 2" model 14, I don't have, with the short bbl and fixed sights it fills the role of a snubby. Are you sure it is 2" and not 2.5"? My 2.5" bbl stays on it most of the time and I conceal it under a sport coat in a Safariland Klipspringer holster in the crossdraw position.
The .22 pistol pac is for practicing for all this. You know the 22 ammo was so much cheaper. Nobody ever thought about dry fire practice back then, or at least we never talked about it. You would go to the range with the duty rig on and run all your drills with the .22 and then put your magnum back in the holster and go about your business.
My respect to your friend's dad, I guess? He had it down with this equipment. Maybe your friend is now liquidating an estate that included these guns? Just guessing.
Best Regards!
BrianD