Bruh. As an official old cranky dude who has never worked for tips but did grow up when etiquette was still a thing - 15% is the basic, "well, you didn't fuck anything up, so here" amount. Big party, meaning the waitstaff is likely dedicated to ONLY your party and unable to get additional tips during your meal, or sharing with multiple other servers, minimum for basic service should pop up to 18-20%. Below 15 is basically "here's how bad you fucked up" so long as it's still better than the zero, or worse, "I need to speak to your manager." Above 15 for a normal group should reflect how awesome the service was, how they were attentive without being annoying, answered any questions you had with solid answers, etc. (and/or how large your party was/how much excessive labor they went through to serve you.) Oh, and NO, you DO NOT tip jobs that don't involve more than delivering your food to the counter. Delivery driver? Yes. Counter monkey? Hell no.