Note that there's only 625 minutes of working during this "15 " hours work day. So working 5 days a week this is less than 60 hours of work per week.

... Without breaks. That's more or less insane. However that's easily adjustable, the article is the same if we read half that number.

It's the complete absence of influence of other people (be it in the form of SOs, kids, coworkers, office environments, meetings, bosses, customers, what have you) that makes it alien to me.

If I could have 4 hours of real, concentrated, productive work on important things each working day, I would massively increase the impact of my work.

https://guzey.com/personal/how-to-use-your-wife/ :-)