There are 18 15-letter words that start with 'mu'.
Note: These 18 15-letter words that start with 'mu' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with mul, mus, mut, mur, muc, mud, mun, mum, mug, muf, muz, mue, muj, muo, muk, muh, muu.
3-letter words start with 'mu' (6)