I think 15% percent is bullshit. If you think about it, the amount of your food depends on the amount. It isnt any harder to carry one plate of food versus another. Or if you have alot of people with you. All of thier food will raise the tip even higher. The waitor or waitress it already coming to that table so there is not really that much more work. I think 5% does it. Maybe less dpending on the quality of service.