[atomashpolskiy]

> I've been interviewing non-stop for a few months. For a few months prior to interviewing I watched computer science lectures online, read CTCI, and had a premium Leetcode subscription with a good amount of practice.

> I haven't done mock interviews with a friend, but I did pay for a few mock technical interviews.

Chances are that, given such extensive preparation, it's not really the technical part that is the problem, if you haven't been able to get an offer after going through a full process at 15 companies. Of course, it might be a severe case of bad luck, but I'd bet that your anxiety and stress are somehow leaking through. Did you self-reflect on that, and if yes, what are your thoughts?