Section 654. Interest shall not exceed 15% per year; when a higher rate of interest is fixed by the contract, it shall be reduced to 15% per year.
Section 655. Interest shall not bear interest. The parties to a loan of money may, however, agree that the interest due for not less than one year shall be added to the capital, and that the whole shall bear interest, but such agreement must be made in writing.
Commercial usage for the calculation of compound interest in current accounts, as well as in similar commercial transactions, are not governed by the forgoing paragraph.