Δεκαπέντε πόντοι is not excepted as an optional translation. Is it too colloquial?
Well, without context πόντοι = points, so it's better to stick with εκατοστά. (And, for the record, the full word is εκατοστόμετρα! But it's a mouthful and not used at all really.)
Πόντοι is just fine for speech in a non-professional environment. I think most people use it. In written form and for professionals like engineers, teachers, etc., εκατοστά is more common.