You mention late Christmas season. A lot will depend on exactly when you plan to be there, and how ambitious you want to be.
Some days are much more crowded than others, but with Express Pass, you can make it work, even on the most crowded days. Are you going to get one-day passes for both IOA and USF? It will be quite pricey for one day, but if you arrive at rope drop for the park with Early Park Admission and stay all day with Express Pass, you can pretty much do everything you'd want in one day (except you'll either need to skip Hagrid or do Hagrid instead of a few other rides). But it will be an exhausting day with a lot of time in lines.
The first question is which park has Early Park Admission. E.g., if USF opens an hour early, you can do Despicable Me and Gringotts then walk all the way back to the IOA entrance for rope drop, then either brave the Hagrid rope drop or walk the other direction back to Pteranodon Flyers (which doesn't have EP), then do the big IOA stuff at the back, circling from Forbidden Journey and Hippogriff, back to Jurassic Park, Skull Island, Ripsaw Falls and Bilge Rat Barges, then through Marvel (Hulk, Dr Doom, and Spider-Man), then either circle over to Seussland or exit IOA and go over to USF.
This all depends on having EP. With EP, the big, exciting roller coasters (Hulk and Rip Ride Rockit) will mostly have less of a wait than the most popular simulators or even Hippogriff, which is a kiddie coaster. Hogwarts Express is great but takes maybe 30 minutes total to experience even with EP on crowded days, so you should think of it as a ride, not transportation.
With a 14-year-old and only one day, I might skip Despicable Me (in my boys' opinion, it's the least exciting of the many simulator rides) and Pteranodon Flyers. I'd still try to work in ET and Seussland, but if the 14yo just wants to cut those and ride Hulk five times instead, that is understandable.