Yes. Smith and Wesson revolvers manufactured from the approximately the mid 1950's onward are rated for plus p ammunition. Your handgun falls well within this range.
Just purchased a beautiful K-38 Combat Masterpiece model 15-3. It's blued with a 4" barrel.
My question is, can I fire +P ammo through it safely?
Yes. Smith and Wesson revolvers manufactured from the approximately the mid 1950's onward are rated for plus p ammunition. Your handgun falls well within this range.
You will have no problem shooting +P in that gun .