The Department of Revenue, with the approval of the State Treasurer, is hereby authorized, at any time after the first settlement of any account between the Commonwealth and any debtor thereof, if the department deems it conducive to the public interest, to compromise with such debtor or his surety for the payment of the debt by instalments: Provided, That the amount of the debt be not lessened, and that the security be not impaired, and that the principal, with interest, together with costs, if any, be paid within seven years subsequent to such compromise.