Sanders is correct to the extent the minimum wage should be raised to adjust to inflation and thereafter should be indexed. However, such an increase is not near $15.00
Most important is that he misleads about who earns the minimum wage. It is a very small segment of the US workforce. Most are not married or heads of families. Most are young and work part-time.
The answer is not trying to solve economic problems by raising pay for rapidly disappearing low-wage jobs, but to get people into better jobs. He does not think through the broad implications and counterproductive effects of going to $15.00 an hour. And by the way, a couple earning the minimum wage each are low income, but considerably above the poverty level.