The 15 dollar minimum wage also has a very insidious trap laid within it. If you raise the minimum wage to 15 dollars under the framework of "providing a living wage", what you're really doing is putting a cap on wages for low-end workers. The result is counter-intuitive to the general belief. If everyone at the bottom has to be paid such a margin-crushing amount, not only are staff and hours going to be cut like you and others suggest; you will ensure that those people remaining that do have jobs will never see another raise again. There will be no path to a higher wage or a promotion with better pay because by virtue of the justifications being used the employee is now "taken care of" and has enough income to cover their costs.
Class mobility in the upward direction will be diminished. Workers' rights will be diminished.
A minimum wage increase at the national level the likes of which is being suggested will kill the notion of working hard to get a better deal. You'll simply be working hard and you had better be happy you still have a job because you can and will be replaced the moment you step out of line or have the audacity to ask for more money. It puts a cap on how much the lower classes can earn and are allowed to earn.