I was looking at transposition chart (lists the interval distances between a transposing intruments and concert pitch).
It lists abbreviations. Examples: M6, m3, 15ma
I figured "M6" ment major sixth and "m3" ment minor third, but what does 15ma mean?

The composition forums are always dead.

15 is two octaves

I believe 15ma means the instrument plays two octives above written pitch.

15ma refers to the 15 steps it takes to move a note up 2 octaves.