I think raising the minimum wage to $12 is more reasonable than raising it to $15. Raising the minimum wage to $15 will result in more unemployment as a result of businesses laying off more employees just to afford to stay in business. This results in less people being able to afford to buy goods at the grocery store and shopping malls. This in turn will further depress our economy because when people buy goods, this stimulates the economy. The opposite is true when we spend less.
This still doesn't factor in inflation and the value of the dollar (based on the consumer price index). The CPI is directly correlated with the value of the dollar and further has an effect on wages.