Based on the Pythagorean theorem, in a right triangle, the sum of the squares of the two shorter sides is equal to the square of the longest side. So, we can use this to find the possible values of the third side of the triangle.
The two given sides are 15 cm and 17 cm. We can label the unknown side as "x". Then, we can set up an equation:
15^2 + 17^2 = x^2
Simplifying this equation, we get:
225 + 289 = x^2
514 = x^2
x = sqrt(514)
Therefore, the possible value of the third side that would make it a right triangle is approximately 22.72 cm.