I did a medical test at a universaty hospital and i should hear untill about just under 17kHz about a year ago. I do this testing every 3 years as part of a study program since my early youth when i had trouble with hearing very high frequencies. I could not watch the tv set of my parents because of a resonance at 19kHz that nobody else heared.
But it's true most of adult age don't hear above 15kHz. The reason why they started testing me was because i'm an exception, and no it's not a gift, it's a curse to hear that good. I sounds so silent that almost nobody hear them, like i hear insects in my bedroom (that everybody have but nobody notice) during the night, i heared resonances from electronic equipment that nobody hears (but with age that luckely disappeared) and i'm very easely sesitive overloaded by general noise (I ran from the city for that).
That test that i do regulary is a real calibrated test. This youtube video is not at all. Like said youtube compression takes out a part of the very high frequency and the volume is not constant. These kind of tests also need to be done with a calibrated headphone in a silent room, not on whatever is connected to your computer in your noisy enviroment. So take the result not to serious. But take the message that it wants to tell serious, for most frequency response above 15kHz is not that important anymore as they can't hear it. Even at 10kHz it's not that important.