There are 104 15-letter words that start with 'de'.
Note: These 104 15-letter words that start with 'de' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with dec, des, def, dem, dep, del, det, den, dea, dev, der, deb, deg, dee, dei, dew, deh, deo, deu, ded, dex, dek, dej, dez, dey.
3-letter words start with 'de' (9)