If I am not mistaken, it is about the same probability of hitting a 1000x Plinko ball. Not that rare if you ask me to categorize it as, 'statistically unlikely'. It all depends upon the number of total bets placed by any player.
One more thing in my opinion, winning 15 hands in a row in Blackjack has even less probability compared to losing 15 hands straight because of house edge (feel free to correct me if I am wrong).
You asked AI what is the probability of 15 straight losing hands but the player in question has won 15 straight hands

, I can understand as we usually have the habit of calculating from the loser's perspective

Yeah I asked about the odds of losing 15 in a row because that's what happened to me and I wrote about that as well.
I mean I have had 15 losses in a row once, never touched that game again after that.
The chance of winning 15 in row is lower of course since the chance of winning a hand is roughly 42% while losing is around 49%.
I think plinko odds are even worse, but I never touched that game anyway.