To enforce the collection of delinquent taxes pursuant to Section 6.30 of the Texas Property Tax Code, it is hereby provided, as authorized in Section 34.07 of the Texas Property Tax Code, that taxes that remain delinquent on July 1 of the year in which they become delinquent shall incur an additional penalty in the amount of fifteen percent (15%) of the amount of taxes, penalty, and interest due, to defray the costs of collection.