Kind of subjective depending on the shooter's ability. The standard distance accepted in many CCW license tests is 7 yards, almost 50% further than your minimum for less than a 4" barrel. I don't have any trouble hitting center mass on a B27 silhouette target from that distance with my short barreled guns like an LCP, LCR, CM9, Charter DAO Bulldog, or Judge PD Poly. In fact, because of the set distance of the first target holders at the range I often shoot at, my practice distance is twice the 15' mentioned. I see no difference in my accuracy at 7 yards, or 10 yards. Even at 25 yards most hits are somewhere in the area of the target that would be very painful, if not immediately incapacitating.4" for me. Anything less than that is kind of useless for anything more than about 15 feet away.
Yep, I regularly carry a Smith M60 with a 3" bbl. and adj. sights. Zeroed for 25 yds, I've killed a cpl. woodchucks in our garden. SA with a two-handed hold, I can keep a cylinderful, slow fire, on a tennis ball at that distance. It's a matter of practice, and severe concentration on sight alignment.It all depends on what distance you are talking about.