Did you tap 15 times and walk off the mat of your own will? Then that's the exact number of times you should have tapped. Tap early, tap often and the lesson you learn is not that of toughness, which is a natural lesson in grappling, but that of prevention.
Prevention of tapping is better than toughing it out. You will learn toughness and it will be thrust upon you, multiply this the smaller the practitioner.
Did you tap 0 times and find yourself exhausted, blood drained from your face from the choke your ego forced you to endure, or the armbar that left you unable to roll the next day, week, month?
You learned nothing.
Apart from your threshold for oxygen deficit and for pain. This is not an ongoing lesson that bears as much fruit as the lesson of becoming self-aware about why you got in the situation, not surviving it.
Chess players analyse the board not for a quick, cheap finish, but seek to outsmart and outclass their opposition. The opposition on the receiving end of a “check’ with their king in danger doesn’t brag at their toughness when they evade the situation, nor should you take similar pride in being outclassed and outmatched yet refuse to accept a defeat you invited.
So how often should you tap?
Every single time you are checkmated.
When shouldn’t you tap?
When you functionally recognise attacks, danger and deconstruct an incoming submission.
Being a white belt, a novice, a beginner, is a marathon of disappointments if your sole purpose on the mat is to tap or be tapped. Maturity of learning in a grappling context comes when the end goal is not to defeat, but to learn and craft your own passage thought the jiu-jitsu art.
Master Helio Gracie, the godfather or Brazilian Jiu-Jitsu, rolled well into his nineties not with the purpose to win and defeat those he met on the mats, but to remain defensively uncompromised. So if the master can do it util the years before his passing, so can you, but start now.