If you can double tap then you can conduct multiple target drills. Post-It-Note’s (PIN’s) are great for this. Put 3 PIN’s at random locations on a standard B-24 target. Double tap each one and move to the next.
FWIW And I don’t care if they are acclaimed USCCA gunfighters I can find NO, ZIP, ZERO, NADA (to quote @Dawn) reason to dump 15 rounds on a single target and go back for one more in a defensive or even a combat environment. Dare I say in a court of law you are in a world of hurt and will be the poster child for large mag bans.
Reloading in the middle of your magazine means you have found cover and want a full stack. DO NOT practice dumping a mag for the sake of a DRILL. Design your drills to incur an empty magazine condition with a full magazine, add targets.
IDPA & 3 Gun are one thing where you introduce “SCENARIO’S” practicing for self defense is another. Don’t let the “Game” interfere with reality.