Tipped min wage in the US is $2.35/hr, and less in other parts of the world that still tip. The menu price covers about 35 cents worth of service outside of really high end restaurants (and these will invite you not to return if you stiff on the tip). That doesn’t even cover the 4 mandatory visits from staff: seating, orders for 3 max, service, and billing. 15% is the rate for regulars, ie you are in 3+ times per month.
If you can’t afford to pay for service don’t go out to eat, get take out.