The answer was in the question. If a person can not effectively engage at 7, 10 or 15 yards, then the problem is a lack of skills and not a question of distance to practice. The ballistics won't change meaningfully between 7, 10 and 15 yards.
The fundamentals won't be learned from a video tape, a Marine Corp. drill instructor yelling at you while doing linear drills on a flat shooting range , learning the "five count draw" or jawing on the internet.
The shooter has to understand movement, human biomechanics, shooting fundamentals, the operation and reliability of his firearm. Personally, I know trainers who can have a newbie shooting better than 90% of the LAPD graduates with just about 6 hours of instruction. However, that skill is lost almost immediately if not constantly reviewed and practised flawlessly.
You have to think! If a person is still at the mindless stage of double taps, two to the chest and one to the head, and other patterns of thinking, he is going to be down on the food chain. It is not a matter of whether practicising a 7, 10, or 15 yards static is better. You need to be able to MOVE and do the shooting at those distances from strong side retention and in low light. So go, buy the $12 dark welder's goggles, start shooting at your indoor range with one foot in the air to simulate movement. This is something that you can do now. If you don't, then you are not making the effort.