Congratulations on your acquisition! Looks to be about 1965 and yes, certainly pre-82 for the barrel pin. Although there was a transition.

A couple of simple use/wear indicators besides tightness, but not infallible, are use scratches on the ejector rod, which appear minimal in your picture. Also, imprints of case heads on the recoil shield when you open the cylinder, esp. around area of the firing pin. Finally, gas cutting on the inside of the frame top, just aft of the barrel

If you don't happen to have one, you can look up Big 45 Frontier metal cleaning pads. You may find them beyond helpful in removing rust, with a preliminary base of light oil before touching with the pad.

Grips are a matter of personal preference - and you may wish to try several, part of the joy of having a Model 15!