California's unemployment rate was 3.9% before COVID, which is only slightly higher than the national rate of 3.5%, which might indicate that $15/hour wasn't that big a damper on employment, unless you make the argument that Alan did that all the people that weren't worth $15/hour became drug addicts and ended up in jail, taking them out of the employment pool altogether. It is unclear to me that if a company were willing to pay someone the going rate of $15/hour to sweep the floor, how anyone could not be qualified to do the job.
The way unemployment is measured, is that a person still has to be looking for a job to be considered unemployed. If he's out of work and has given up looking for a job, which many young people and poor people have reached, then they're not counted in the unemployment rate. There are millions of out-of-work people like that who are no longer counted as unemployed.
Regarding not be qualified at $15 has to do with too little productivity. Regardless of the job, some people are more productive than others. So an employer is not going to pay $15 to a person who can only produce value worth $10. So the less productive in society can't get a job because the minimum wage has priced him out of the marketplace. Had the employer been allowed to hire him at $10, they would have knowing they're getting $10 of productivity from him. So instead, they'll find a employee, maybe a college graduate who will greet patrons as well as sweep the floor, that is providing $15 worth of value.