If you are asking for a Pythagorean triplet in which one number is 15 then ...
One of the earliest known Pythagorean triplets is (3,4,5).
Simply multiply by a constant (integer) value, and you have another Pythagorean triple.
In this case, multipy by 3, to give (9,12,15).
Or, multiply by 5 to give (15,20,25).