I have 3 older boys too. In fact they are 17, 21 and 22 now, but if i think back to what they used to eat i will answer you.
So i will do the 17 year old as if he were 15 again. Its pretty bad tbh. For reference we are what you might call an educated, fairly wealthy family. Boys all went to private school, if that makes any difference.
Breakfast, either nothing or if we were early getting to school a McMuffin meal.
Tuck shop at break, probably crisps and or Sour Chews of some description.
Lunch was good at their school - nice choices of fairly healthy things like fajitas or stews, jacket potatoes etc.
After school he would plough his way through absolutely loads of crap, multi packets of crisps, bananas, Club biscuits, yoghurts etc.
Home cooked dinner, like a curry, or pretend nandos or lasagne.
Then after we would go to bed there would be evidence of bowls of cereal being consumed whilst xboxing.
It all sounds really bad, but this child is STICK THIN!! I no longer buy crisps and the like as he is the only one left at home now and is working (apprenticeship) and earning and buys his own rubbish. We get Hellofresh boxes now so eat pretty well, but i often hear a pizza delivery arriving in the evening after we have all eaten. He just never seems full and is still skinny. (6ft 1 and with a 28 inch waist and size M mens tops).
I fi fed him carrot sticks and cherry tomatoes in a packed lunch he would have wasted away! lol.