In a right triangle, the side lengths are typically denoted as \(a\), \(b\), and \(c\), where \(c\) is the length of the hypotenuse (the longest side). In the Pythagorean triple (9, 12, 15), the side lengths are given as 9 and 12 for the legs, and 15 for the hypotenuse.
Thus, the value of \(c\) is:
\[ c = 15 \]
Therefore, the value of \(c\) is 15.