“then the waiter expects a tip for merely doing the job he’s already getting paid to do”
Waiters get paid far below minimum wage because they receive tips instead. How do you not know that?
“they receive tips instead”
As usual, you fell into that one. If, as you say they’re working for tips instead of a wage, then they don’t need $15.
That is true is most of the country. However, California is different. In California, tipped employees earn minimum wage plus their tips. Under California law (different from the federal law) the tips belong to the employees, and employer cannot use tips to offset the employer's own obligation to pay the minimum wage.
As of January 1, 2017, for employers with more than 25 employees, the California minimum wage increased to $10.50 an hour. That includes tipped employees.
http://www.dir.ca.gov/dlse/faq_minimumwage.htm
This article refers specifically to employees in the city of San Diego. The minimum wage in that city is higher still, $11.50 an hour, due to a ballet initiative that passed in June 2016.