The correct answer is 15.
Originally, Pongo and Perdita has fifteen puppies in their litter. We only know the names of some of them: Patch, Lucky, Rolly, Penny, Freckles, and Pepper. However, over the course of the movie, Cruella de Vil and her 'gang' steal the puppies in order to make her expensive clothing out of their pelts. Luckily, the 15 puppies manage to get saved, along with 80+ other puppies that were kept in Cruella's captivity - that's why the movie is called 101 Dalmatian.