If you need 15 letter words that start with A right now, you should look at this page, it contains a lot of words that contain 15 letters starting with A...
NB : You can also browse 15 letter words that start with A and other letters or 15 letter words ending in Z or something else...
The website LetterWords.net allows to browse words by the letters they contain.
For example, you can get 3 or 4 letter words that start with A and ending in O... possibilities are endless and these kinds of searches can be very useful during a crossword puzzle or a scrabble game...
To browse all these valid english words proposed on the website, you can use the alphabetic navigation bars or try the words search engine just below, this one will be more convenient if you already know some letters of the word that you are looking for.