Doesn't matter what you agree with or not,
in France (and I believe it is French law) the Service Charge is already included in the prices on the menu.

In France, the French do not tip in the american sense of the word. If so inclined they do leave a "pourboire" in cash, but this is never 15% or more. Try maybe a few euros or maybe 5%

So the restaurant mentioning a 15% service charge is being very misleading to Americans, the French would just ignore it.

So if asked if Service Charge or Tip is included they will almost always so no, for in their translation you are asking about the "pourboire" being included, which it never is. There is a big difference ($) between an American tip and a French pourboire.