I don't know where they came up with the $15 number, but I do believe, based on my personal experience, that they should index the minimum wage to inflation. Let me explain:
I was working for the min. as a kid. Then along came "circumstances" that caused inflation to zoom up (think 10%+). So there I was, making $2.30, (sidebar: which according to the BLS is $9.55 in today's dollars) and all of the sudden - BAM - all the prices shoot up. Suddenly I can't afford a 'tank of juice' for the 'ole Rocket 455 - if you know what I mean...so there I am, reduced to joining 'mad max' in the Australian Outback...
All because the min wage is not indexed to inflation. If it were indexed, and, $9.55 today, we probably wouldn't be having this conversation and I wouldn't have been forced to participate in that 'thunderrun' in that tanker with Mel Gibson!