Hmm...kind of a weird question.
What is the value of a business? To maximize the value of said business.
My dad appraised a car dealership recently and the guy was stressing about the minimum wage increase as his (commissioned) employees would have to get a higher base pay in slow periods when they aren't selling as many cars. If you look at the cost-benefit analysis, the owner has optimized the number of employees to maximize the income to the business. At a higher minimum wage, he would lower the number of salespeople on the floor, resulting in a decline in car sales, and consequently, business income.
Most aren't questioning whether McDonalds has a viable business model (that I know of). But if minimum wage increases to $15, you might see a shift to automated ordering kiosks and even increased automation in food preparation, due to the availability of technological alternatives and their respective costs.
In the example of my company, the college kids aren't staying for extended periods, and they have to be trained for a portion of that time. Have their been some past college kid employees worthy of $15/ hour? Yes - maybe more, and we would've kept them as long as they wanted to stay but they've moved on to bigger and better things than a part-time helper. We're glad for them too. But, there's also been multiple past employees that didn't bring any value and weren't worthy of minimum wage. If the value that the workers bring isn't $15/ hour or more on average, the business model would indicate that said position would need to go unfilled.
I am aware that Amazon is hiring its workers based on $15/ hour. But, Amazon is also a potential future anti-trust target and is regarded as the symbol of online businesses killing the mom-and-pops. If they were to hire as many minimum wage workers as they could, the opinion of their corporate brand would be further despised, so their business model supports increasing employee pay to maximize their corporate image.