I will agree that the situation is a little ridiculous. However, at least in the US, the general expectation is that this is how it works, and failing to account for and including that additional 15% is cheating the waitstaff. Would it be easier if the food were just 15% more expensive? Sure, but it's not.

That said, most of the waitstaff I've known would rather get tips than work for a base salary. Customers are, generally speaking, going to be more generous than employers.