Tambarina Restaurant
Adding tips

Hi,
I would like to know if it is legal to add just 15% to the bill as a tip.
The normal norm is 10%, that is if you are happy, but I was 2 weeks ago in that restaurant and they just added 15% . I was with guest so I did not want to make a fuss about it, but sure I WILL NOT GO BACK there. This is an illegal operation and, maybe they took advantage thinking we were overseas tourists,
so, let me know.