At 15 dollars and hour, there would be no legal employment in the US for a huge chunk of the population. Australia has chosen to keep those people on the dole, but this doesn't fly in the US politically. So, a lot of people would be forced into, I guess, drug running and prostitution, since every other employment would have been legally prohibited for them.
Eh, for the time being that would be true. But small businesses would get crushed & inflation would do its dirty work, so that $15 in several years would be worth $7.25 or whatever the federal minimum wage is today. In other words, small businesses would suffer, the rich would benefit, & the poor would, at best, experience no real change. Why am I not surprised?