56-8-3: Interest rate; no written contract.

The rate of interest, in the absence of a written contract fixing a different rate, shall be not more than fifteen percent annually in the following cases:

A. on money due by contract;

B. on money received to the use of another and retained without the owner's consent expressed or implied; and

C. on money due upon the settlement of matured accounts from the day the balance is ascertained.