There are 23 15-letter words that end with 'sis'.
Note: These 23 15-letter words that end with 'sis' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words end with osis, esis, asis, ysis, psis, isis, ssis, rsis, usis, lsis, nsis, tsis.
4-letter words end with 'sis' (1)