The 30-60-90 triangle's sides share a ratio of 1:√3:2 where the shortest side is the one facing opposite 30°.
This means that the longest side of aa 30-60-90 triangle is twice that of the shortest side. Now, given that the shortest side has a length of 15, then its longest side would be 2(15) = 30.
Thus, the hypotenuse is 30 units.