Since I started this thread in 3/12, I have seen the same question SO many times.
In fact, twice last month.
One concerned a Model 15. Personally, I'll shoot +P all day long in my Model 15 without giving it a second thought.
Since I wrote the OP, I lucked into a "Pre-Model 10" circa 1957. I have no worries using the same ammo I shoot in my Model 15. The Model 10 doesn't seem to mind.