No retailer’s on-sale license shall be issued to any person to whom, or for any premises for which, a manufacturer's, wine grower's, importer's, wholesaler's, or rectifier’s license is issued; and no manufacturer's, wine grower's, importer's, wholesaler's, or rectifier’s license shall be issued to any person to whom, or for any premises for which, a retailer’s on-sale license is issued, except that a retailer’s on-sale license may be issued to a wholesaler in counties not to exceed 15,000 population.