The aggregate amount of taxes that may be levied by the taxing authority of the City without a vote of the people on any taxable property assessed and listed for taxation according to value for all purposes of the City shall not in any one (1) year exceed fifteen (15) mills for each dollar of assessed valuation. Of said total maximum levy, an amount shall annually be levied sufficient to pay the interest, sinking fund and retirement charges on all notes and bonds of the City heretofore or hereafter authorized to be issued without the authority of the electors, which said levy for debt retirement shall be placed before and in preference to all other levies and for the full amount thereof. Of the remaining portion of said total maximum levy, an amount shall annually be levied sufficient to provide the amounts, if any, required by law for police and firemen's pensions, and the balance thereof, but not to exceed three (3) mills, may be levied annually for the purpose of paying the current operating or other expenses of the City.