Agreed.
The minimum wage was based on a 40 hour week But the 40 hour week is a thing of the past. Most new jobs are part time.
We could consider a minimum hours law similar to the minimum wage law - but that would leave a lot of people out of work, because there are just not enough 40 hour jobs to go around.
Automation and offshoring (thanks to capitalism) have already caused a reduction in the number of 40 hour jobs below the needs of the national workforce.
We could chase the dog's tail around a tree by raising the min wage to $15, but most of those jobs will be the first to be automated whether we do or don't. The problem is bigger than an incorrect min wage.
Ultimately, we will have to have a very strong socialism element mixed in with our capitalism because there simply will not be enough jobs. It won't get much better for very long. If it does it will be temporary. The job losses will steadily advance and eventually displace most workers. We need interim steps to deal with the immediate imbalance, and we need to accept that longer term solutions are going to have to include a Universal Basic Income for all - for doing absolutely nothing.
This will be an age of enlightenment because people will have more time on their hands to learn and work out issues.