I could hear 14 but with 15 all I could hear was a tiny click at the start and at the end. Used my headphones.
The first time I tried it all I heard was 8. That scared me. But that was with a bunch of other noises in the room and my volume at somewhat low levels.
I've always had average to below average hearing, so I'm not surprised. I was surprised when I took a hearing test while at an ear/nose/throat doctor visit and he said my hearing was normal. I was also surprised when I saw how much that cost, especially since I had no other medical expenses and I had to pay it directly because of my deductible.