As someone who lives in the US, let me just say that 15% is the minimum tip we pay for acceptable service. Bad service gets 10%, good service 20%. Keep in mind that in the US, waiters get the majority of their pay from tips (often they are only paid a pathetic salary of $2-3 an hour). If you can not afford this tip, find a cheaper restaurant. Like someone else said, just think of this as a mandatory tax.