All good points...I just personally wouldn't answer knowing all the details at only 15. I was 5"11 and 65kg as a kid no dieting...training daily.
People are going to quote me and say "no, no" but the bottom line is that if you're 154 pounds comfy just chilling right now, you're going to want to drain down quite a bit to compete and maximize your advantages. I wish it wasn't the case but that's the way it has always been. Most amateur comps weigh in the day of, I believe, but if you are envisioning or simulating a pro route, it's made even more dramatic by the 30 hours you'd have after weigh in to fight time.
I hear that philosophy but its a short term fix and doesn't benefit in the long run. Sure he might be as big if not bigger than his opponents but then he will probably get by on size and strength, sure you may win but skills pay the bills in the long run. There will always be bigger and stronger foe, so maximize skills and not physical advantages as a kid