It's not the role of government to tell companies how much someone is worth, that is the job of the market.
The real minimum wage is $0 - if you try to force companies to pay someone who is only worth $10 to them, $15 instead, they will be fired and / or replaced by robots.
Raising the minimum wage raises inflation and prices - the poor will never earn more in real terms even if the numeric value of their pay denomination goes up, as all the things they want and need to spend that money on (assuming they keep their job) will also go up.
At a time when stimulation the economy and improving employment is most needed, putting further limits on employers and making it harder for them to keep staff is simply idiotic.
It also doesn't factor in location - $15 per hour in NY could be nothing, but significant in some small town in the middle of nowhere. Why have one-size-fits-all when it clearly doesn't?