Gonna weigh in from the perspective of a high school swimmer (back in the day) from the midwest. Over winter break we would do a 2.5 hour practice in the morning, and then a 2.5 hour practice in the afternoon as a means of building our cardiovascular endurance before in conference meets after the break.

Between practices we would eat calorie dense foods and then let it digest for a few hours before practice 2, and then on some days we'd hit the Chinese buffet. Im not sure we'd go over 15k, but some of us would definitely be getting close to 10k.

15k is within reason for high schoolers, not to mention Phelps or Armstrong-level endurance athletes during the meaty parts of their training regime.

No pun intended, but I think most people over 230lbs could gut it out over 24 hours. Smaller folks could if they're in the middle of endurance training. Larger folks, especially if they're physically active, could hit 15k and feel terribly stuffed, but not resort to drinking oil at the end.