Mike is correct, because the rules for powers and exponentiation say that when you elevate a certain base which is already being elevated to a certain power, the powers multiply.
This means that:
[tex] {( {a}^{b} )}^{c} = {a}^{bc} [/tex]
Or, using your example:
[tex] {( {2}^{3} )}^{5} = {2}^{3 \times 5 } = {2}^{15} [/tex]
