Ditto on what Sipsey river and Robertfishes have said. Start close no more than 10 yds so as not to break an overly weak shaft, adjust length for good group and gradually move back, I go back to 25 total but leave the shaft weak at 20, about 2 inches right of fletched seems to work well for when I switch to check with broadheads. Periodically checking with a bare shaft also helps you check your tune/form.
If your tuned well and have good form the arrow will be flying well shortly after leaving the bow, the bareshaft proved it to you, so 15 yards is no problem.