Section 15D. Notwithstanding any general or special law to the contrary, a city or town that accepts this section may apportion all future sewer assessments or unpaid balances of assessments over a period not to exceed 30 years, and may structure the payments so that the amounts payable in the several years for principal and interest combined are as nearly equal as practicable. These equal payments may be further apportioned and collected by the city or town on quarterly tax bills at the option of the city or town. An owner of land assessed may pay the total remaining principal amount due without a prepayment penalty.