Sum of the squares of first n even numbers = $\dfrac{2n(n + 1)(2n + 1)}{3}$
Sum of squares of first 15 even numbers = $\dfrac{2 × 15 (15 + 1)(2 × 15 + 1)}{3}$
= $\dfrac{30 × 16 × 31}{3}$
= 4960