This is what Keynes predicted might happen - https://onlinelibrary.wiley.com/doi/full/10.1111/ecca.12439#... That article notes most people can't make enough money from 15 hours of work to save up for retirement. I also wonder if "leisure" has to be redefined, since work and life blend so much online. What does 15 hours of work really mean in a knowledge work job?
For me and I think in the past leisure did not mean mindlesly doing something like nothing, it meant time after misery is gone. I see it as working necessary time at work that you likely do not want to do, like at a factory assembly line or farm, hospital, etc. After that, you can stay at work, but do something else, like engineering at that factory or what else there is you would like to do. This mean less working hours, more people could get a job, it is something like work sharing. It would allow older people to work too, since work day will be lower, it is not like old people can't work at all, they can't work as intensivelly. In the end, those who do not work at the moment, still connsume, they just do not produce what they consume. With smaller work day, they will be able to produce. By work here I mean work and firms that produce things related to "misery gone", not all there is. So if someone would like to work himself 16 h/day, ok, but not in those firms.