Before the time of payment of said assessments or any installment or installments thereof shall be extended and before the board shall institute proceedings for the issuance of drainage refunding bonds, the owners of not less than fifteen percent of the land within a drainage district as shown by the transfer books in the auditor’s office upon which drainage assessments are unpaid, shall file a petition with the board requesting the extension of the time of payment of assessments levied in said drainage district or of any installment or installments thereof, setting forth the date said assessments to be extended were levied, the aggregate amount thereof unpaid, and requesting the issuance of drainage refunding bonds, stating the amount and purpose of said bonds.