Folks in the military do 84-hour work weeks when deployed (twelve on/twelve off — and really, with 30-60 minutes of handover time factored in it works out to 91-98 hours/week), and are deployed for up to a year. It's brutal, but it is sustainable. Having no other responsibilities to think of probably helps; I've no idea how distracting modern communications technology is to folks with families.
I'd sure as hell would never want to work with them.
I assume this also means the responsibility to keep one's health in check is sacrificed for additional workload?
I can't imagine keeping up an exercise routine working that many hours.
Not everyone means the same thing when they say something like "15 hour work day". That said, I think short busts of non work specific activity without changing your surrounding is no substitute for changing your surroundings and context enough to switch gears for a while. A trip to the local coffee house with coworkers where you still discuss work is a poor substitute for an extra 15-30 minutes at the end of the day where get out and do something entirely different.
But what happens to your health? How can you exercise and eat healthily? Go for a run on your only day / half day off?
Your future self will be angry at your past self when it sees what you've done.