What percentage of the population makes less than $15 per hour?
It depends primarily upon location. Well, in the world in general too of course, however specifically I refer to locales such as one of the tiny towns near where I live.
I have to laugh when I think of anyone locally attempting to strike for higher wages here. As soon as anyone tries it, there will be a line out the door of the building where the business is located with others applying for that position and happy to have found work for the pay offered.
Speaking as someone tasked more than once with hiring qualified individuals for necessary work: I am not paying 50 dollars an hour simply for someone to read the test equipment and write down the results. Neither, as a businessman, will I pay some pimply-faced kid fifteen or even ten dollars an hour to stand there and make change at the register. No bloody way.