Around here an average meal at a restaurant would be about $14 lunch and $18 dinner per person.
So to make the often promoted $15/hr wage, the server would need to clear $96 in tips over the base wage of $3/hr. At an average of 18% tips that would mean the ticket revenue would need to be $534 for the shift. @16 avg per person that is about 4 people per hour, or 1 or 2 tables per hour
If the restaurant is that slow, that the server is only serving 1 table per hour, well chances are the server needs to look for another job anyway because that place will not be in business very long.
This is also why alot of servers I know prefer the tipped model over a higher base wage, if a strait 15/hr wage was created with no tips, many servers would make LESS money then under the current system
Most of the people calling for a $15/hr base wage have a delusional belief they will make $15/hr PLUS tips... that is never going to happen