There are 12 15-letter words that start with 'supers'.
| supersaturating | supersaturation | 
| superscriptions | superspecialist | 
| superspectacles | superstimulated | 
| superstimulates | superstitiously | 
| superstructural | superstructures | 
| supersubtleties | supersymmetries | 
Note: These 12 15-letter words that start with 'supers' are found from the USA & Canada version of the tournament Scrabble word list.