the underlying formula that you want to use here for compound interest is
A = P(1 + r/n)^(nt)
for this scenario that means taking
A = 15000(1 + 0.065/n)^(7n)
so you would just plug in the value of "n" based on the compound frequency that you are trying to measure ... annually means n = 1, quarterly means n = 4, monthly means n= 12, and so on