I'm not naive but saying that 'smoking pot is not a problem' at age 15 strikes me as wrong. Look, a lot of us did it at that age but that doesn't make it 'no problem'. There are definitely physical and mental consequences for any kind of drug use although many of those consequences are reversible and not permanent. For a 15-year old, I'd be surprised if, in extreme cases, those consequences are potentially worse than for a 25-year old. However, for a huge majority, smoking pot or drinking at that age truly is a phase and it does turn out to be a non-issue. But, for others, it develops into a huge problem.
The decision making ability shown by Bronny is highly questionable. I'm guessing being LBJ's son doesn't require a lot of 'look at me' as he's under scrutiny 24/7 anyway. But, posting something like this on social media at his age makes me question a lot about his thought process. Phase or not, when I was his age and doing similar things, the last thing I was going to do was advertise it for all to see.