Though I do agree that $15 is too high. Somewhere in the $9-10 range would be more reasonable. Why? Because anyone who is not intellectually disabled (the disabled have special min wage rate) and has completed the requisite 10 years of education can perform labor valuable enough to earn it.
Yes, even if they are "just" slinging hamburgers. I knew an immigrant woman who had only 3 years of formal education and was sadly barely literate, but she could do the work of three people when she worked with me at my first job (Wendy's).
I would say she single handedly brought in $4000/day.
Do you think they paid her more for it? No. Why? Because she couldn't make them.