Are normal adults not "working" in a similar way to your kid for 15+ hours per weekday?
Comparable adult parent things would be up at 6am, prep kids for school day, in the office by 8am, 8 hours of work plus a lunch, departing the office around 5pm, transporting kids to/from some activities, dinner, helping kids with homework, somehow fit in regular shopping needs (food, essentials, etc), maybe some volunteering or hobby things, if lucky in bed by 10pm, and we're easily at 15 hours of "work" on a weekday.
Comparable adult parent things would be up at 6am, prep kids for school day, in the office by 8am, 8 hours of work plus a lunch, departing the office around 5pm, transporting kids to/from some activities, dinner, helping kids with homework, somehow fit in regular shopping needs (food, essentials, etc), maybe some volunteering or hobby things, if lucky in bed by 10pm, and we're easily at 15 hours of "work" on a weekday.
Yes, it's a lot.