The Problem with things, like the 15 hour per week claim, is that work isn't comparable in different forms of society.
The article for example never specified, what it defines as work. Is only the time spent hunting or foraging 'work' ?
Is making & maintaining tools work? Is learning a new skill from an elder work? Is experimenting with a new technique work? Is keeping the campfire alive work? Is keeping watch for dangerous animals work? All of which are work in today's society. Hell, over half of my work week is spent 'socialising'. Do I only work for 20 hours a week now?
Every article or study, that I know of, that claims that people in the past worked significantly less, fails to specify what it defines as work.
What are you basing this statement on? All analysis I have seen so far come to the conclusion, that the war is devastating on an humanitarian and demographic scale, but sustainable for years to come from an pure manpower & training-capacity pov. (Given historical data)
The same analysts suggest that the main reason for the current stalemate is the lack of weapon systems/munitions, that would enable a sustained breakthrough like artillery, tanks and air defense systems. Stuff that western allies hesitate or are incapable to provide in large quantities.