Raising min wage to 15 bucks will only increase the percentage of those living below the poverty line. The only way this would work is if everyone got the same raise.
Joe the plumber makes a decent living at $25/hour. Minimum wage is raised to $15/hour and all employers affected by this increase raise their prices to pay the new min wage. Joe still makes $25/hour but his money is now effectively worth $15/hour. Joe realizes he was an idiot for voting demoncrat.