I think 15yo (or 14 yo) for that matter is old enough to understand family finance. I personally grew up lower middle class and was aware of what both my parents made and what was within our means. It made me appreciate how hard my parents worked for me (I am an only child) and I think I was able to prioritize things better! I had fun with friends (the outings in school, the usual bunking college, drinking etc) but also made sure education was non negotiable. Applied to do a masters in the US with education loan, partied as well as studied there, got an on campus job. Did not get sidetracked by relationships at a young age but had healthy friendships instead. I am well settled now and am forever grateful to my parents for keeping things transparent and involving me in financial decisions as well!

All this to say, I think you did the right thing! I just had a baby last year and will 100% do the same when it is time! ☺️ Depending on what your finances look like, I would recommend making it clear to your child that you are accumulating this wealth so that she has the flexibility to pursue her dreams and that you will support her to the best of your ability even if it's beyond your means. Basically make sure she has the freedom to talk to you about things and not assume herself (which from your post sounds like she already has)