A $15 an hour worker costs a lot more than $15 an hour. That's one of the problems with paying people more. It's $15 + SS + workman's comp + Medicare, and, if they're full time, + medical insurance. Often, you have to add in sick leave along with other sorts of leaves.
Now, if the worker is worth $20 or $25 an hour, that' OK. If they're only worth $10, then the employer has a problem, which is generally solved by hiring fewer workers in one way or another, or by hiring illegal labor.