My nephew will travel unaccompanied minor later this year. We've briefed him to be ready for questions and explained it's so that the immigration know he is safe and being met.

Having talked to some UM chaperones, and also heard solo-travelling-teenagers at the immigration desk, it usually is questions about where they are travelling from, why the minor was there / why are they coming here (establish where parents are), who is meeting them, and if parent 1 is separate from parent 2 a check that both parents are in the know.

I suspect a 15 yo sees this as hassle, a parent probably sees it as a safety net.