A video, is not the best way to test hearing. In fact even using an audio system is just a mediocre way to tell.
The problem with a LOT of audio systems, is that you are not hearing a pure test tone in isolation, and at a specified level in comparison to 1khz.
Often you are hearing artifacts OF the delivery of the tone and other things. From all the things you said you have subjected your ears to, I would find it utterly incredible if you are hearing 15.8 khz anywhere close to the reference tone at 1khz for instance.
My best bet would be far closer to maybe 12-13 khz
If anything, that implies that I can hear beyond that. The tone appearing from nothing was obvious in all cases, just as when I tested them years ago.
Often you are hearing artifacts OF the delivery of the tone and other things.
It's no artifact. It's annoyingly loud and clear and sounds identical from different videos.
A person recently posted the claim, in response to one of my posts, that the evidence shows that hearing damage from noise is focused mainly in the most sensitive regions of hearing. 15K and above are not that. So, it appears that the majority of the degradation to my hearing is likely in the upper mids or lower treble — wherever it is that hearing is most sensitive. My vague recollection is that that's somewhere around 1K, which is why 1K is traditionally associated with things sounding like telephones (as that frequency, or near to it) was chosen for phones due to it being easier to hear.
As for specified level, that is a different matter. Reduced sensitivity is one thing. Not being able to hear a frequency is another. I don't doubt that my sensitivity for 15K and above is reduced. But, something around 15.6–15.8 appeared from nowhere each time, with different videos. Changing the level had no affect in terms of me definitely not being able to hear past 15.8, at least at volumes I felt were safe.