I did want to mention about the various "advice to my past" lemes out there. (leme = lemming + meme). I would neither give advice to myself when I was a senior in high school nor at fifteen years ago.
When I was a senior in high school, I was still on my way down and I really needed to hit bottom before I came back up again. Any advice might've delayed that and that would've been bad.
Fifteen years ago was a very chaotic time in my life and adding extra inputs would've skewed what finally came out of that. I like who I've become and that period of my life was very formative of who I am still in the process of becoming.
One other bit about these "advice to past selves" lemes. I didn't listen to people in the past and don't do so much now either. Why would I then? I guess, if the advice is coming from your future self, you're supposed to give it more weight. I don't know if I would but then I'm stubborn and contrary. Yay!