There are 13 15-letter words that start with 'ob'.
Note: These 13 15-letter words that start with 'ob' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with obs, obl, obt, obe, obj, obv, obi, obo, obn, obf, obd, obb, obc, oba.
3-letter words start with 'ob' (3)