It depends on parents and kids going. Do you know and trust them ? Are you sure her phone will work?
Is your child mature enough to walk away and get help if her phone isn’t working? Yes their should be security at park.
Absolutely not! 15 you know damn well they will sneak out.
I trust my kids but I don’t trust anyone else 15 or 16 is not mature enough.
I think it really matters how much you know and trust the friends parents. My granddaughter has 3 besties she’s been friends with since elementary. They go to high school next year. We know all of the parents and siblings very well. Been with them in several school and sports activities. Been to their homes. Even the grandparents. So we would be fine with her going with any of them. But a friend from school? That we are not familiar with the family? No. If she really wanted to go my daughter and son in law would probably get a room and go as well to have additional supervision. Helicopter parents? Maybe. But it one incident to ruin a childhood. Not worth the risk.