"He who pays the wages makes the rules"
You pay someone for what their level of labor is worth. If these people had some skills/abilities they would apply for jobs that paid 15 an hour or more. They instead, with union backing [all about the unions wanting to organize fast food like they want to organized Walmart], they demand more money that they are worth.
Since flipping a burger, or stocking a shelf can be done by someone who dropped out of ninth grade, it will never be worth 15 an hour. Minimum wage is ENTRY LEVEL, and if you are trying to support a family on that then I suggest you get a second job to up you income, of learn a trade,skill/get further education in a field where your labor would be in demand.