The value of 15C0 2- 15C1 2+ 15C2 2−⋯− 15C15 2 is
15
-15
0
51
As we know that C02− C12+C22− C32+⋯+(−1)nCn2=0
(if n is odd) and in the question n = 15 (odd). Hence, sum of given series is 0.