According to http://smallbusiness.chron.com/profit-margin-supermarket-22467.html, your run of the mill grocery store has a profit margin of a whopping 1%. Can you explain to me how that's supposed to pay for increasing the wages of the majority of their workforce by 100%. Labor is the biggest cost of doing business, pretty much across the board.
All similar business in the same geographical area pay generally the same wages, and so have the same general costs of doing business. As such, any business that attempts to inflate their profit margins have really only one way to do so: by increasing the price of their products. But if they were to do so, they will be immediately underpriced by their area competitors. As such, profit margins of general businesses, not just grocery stores, but all general businesses, tend to be razor thin. They can only charge a bare minimum above the cost of their products, in order to stay in business.
And we're not talking about just your cashiers in the grocery store. The companies that run the trucks that deliver the goods to the store also have to raise their minimum wage too, and will also have to increase their costs to deliver goods, which gets passed down to the grocery stores, which will also have to increase their own prices on account of that too.
The janitorial services, that send their workers to the local businesses, to clean their toilets, will also have to increase their own minimum wages too. This also translates to their direct costs, which they have no choice but to pass down to the grocery store, as their customer, who will also have to increase their product prices on account of that too.
You can come up with a myriad of examples. Do you know who really ends up paying for the $15 minimum wage? You, the helpless consumer. Always.
There's an old term for all of this. It's called "trickle-down economics". Perhaps you've heard of it. Much derided by the radical left; perhaps the term was originally poorly chosen. A better name would've been "real life".