What will boiling hops for 15 minutes give me (besides15 minutes of bittering) that won't happen at flameout?
Will much aroma/flavor be driven off during the 15 minute boil?
In other words, why 15 instead of 0 - or the inverse, why 0 instead of 15?
I wouldn't say this graph is perfect but it gives you an idea of what's going on:
That shows the most aroma coming from a ~7 minute addition, personally I find I get the best aroma with an addition at flameout that's steeped 5 - 15 minutes before chilling.
Seems to me lately people consider anything less than 20min to be flavor/aroma. Both are flavor and aroma is stronger when it's steeped less time.