I don't want to paint all 15-year-olds with the same broad brush. I arrived home from an errand today to find Middle Sister and two friends (one girl, one guy) in the pool. TheDad told me that when the visitors arrived, they came in (without being asked) to say hello before swimming.
We had some grilled hamburgers, baked beans and salad for dinner. The teens ate, talked, laughed, and then bused their own dishes without being asked--politely checking with me to see where I wanted them to put the dirty plates. Before leaving, they both thanked us for the meal and the swim.
Visitors like THOSE are welcome anytime.