both are great events, but i like the Gathering better for being able to hang around a bunch of fbody nuts. the Power Tour has a ton of people with a wider variety of taste and cars so it doesn't have as much of a friendly feel as Gathering does.
i think your 15 year old son would do fine at G14 and have tons of fun. the drunks don't start getting crazy until around midnight and you can get him inside before then if you don't want him to see that. it's not that bad tho. i like to laugh at 'em cuz they usually just run around screaming "wahoo!"... or write little sayings by people cars with sidewalk chalk on the asphalt... or take apart Fbodfather's rental car and see how many people they can stuff in it
it's definitely nothing compared to mardi gras so i may be a bad person to ask about it tho.
the other cool thing about G14 is you really don't even have to leave the hotel. the first year we went we didn't leave at all. they have 2 restaurants, a big pool, and of course vendors at the event. they also have 3 great restaurants just up the street (Mexican, Italian, and Seafood). they also do a tour of GMMG, a cruise to the Varsity (hamburger joint), and other fun stuff like the slow drag competition. so there's lots to do. if you wanna get away, there's also a nearby Coca-Cola plant that does tours.
for me, the difference is definitely the people. at G14, you'll see a lot of people you know from different message boards... and it's all fbody love. and Fbodfather always brings a bunch of cool cars and hangs with people (and signs cars too). at the Power Tour, it'll be a ton of people you don't know, but a wide variety of cars to look at (at least that's how it was for me when i went back in 99) and i don't remember much other stuff to do with the Power Tour cuz i just went to it for one stop and didn't travel with it.
hopefully, all that rambling helps somehow
if you go to G14, we'll see ya there!