What is the value of ‘a’ in the below equation?
$$\left\{\left(5 \times 5 \times 5 \times 5 \times 5 \times 5\right)^{5} \times \left(5 \times 5 \times 5 \times 5 \times 5\right)8\right\} \div \left(5 \times 5\right) = \left(625\right)^{a}$$

A

14

B

17

C

16

D

15