The Auditor, upon the receipt of all such statements from the different Counties, shall, together with the Treasurer, ascertain the amount on each hundred dollars worth of property so assessed ^that^ will be necessary to pay the current expenses of the state, for the current year; and thereupon, the said Auditor and Treasurer shall inform the county commissioner’s courts of the different county[counties] by written message, of the amount so necessary; and the collectors shall collect no greater amount for state purposes, than shall be returned to the county commissioners courts as aforesaid. Provided: That no greater the said auditor and Treasurer no greater amount shall ever be collected under this act, for state purposes, than is provided in the 15^th section of this act.