Applicability of interest rate on late payment of excise duty w.e.f. 01.04.2016

Dear Sir, What is Interest Rate applicable from 01.04.2016 for late payment of Excise Duty, We will be paid Excise Liability for the Month of March.2016, which will be paid on May.2016. Then what is applicable Interest Rate as per Section 11A of Excise Act, is it 15% or 18%.