I usually tip 20%. To make things simpler if a restuarant added 15% I divided the tip in half and left that amount in cash so I ended up leaving 22%. I do find it annoying them adding the 15% but I certainly understand. i was told by a local that American's were good tippers but some tourist from other countries did not like to tip or tip at all. He told me a lot of tourist from Venezuela would not tip at all so it's probably best for them to add the minimum 15% tip. A local also told me water is very expensive and his water bill was $200 a month for a family of 5.