15 minutes isn't much at all I agree. I think for some people they get too much into their head about it. I know in some cases for me I struggled to do exercising at home. But if you told me I had to go to the gym, I wouldn't have an issue with it. It doesn't make a lot of sense but I think how my brain is wired is that I prioritize work or relaxing while at home and don't associate my apartment as "a place to exercise". Walking can work in a similar fashion where people get more focused on working or relaxing that they're not able to get themselves outside.