By Paul Monies, Business WriterResidential electricity customers of Oklahoma Gas and Electric Co. could see their bills rise 15 percent by 2019 under a plan to deal with environmental regulations and the replacement of aging natural gas units at a Mustang power plant. Most of the increase in costs would pay for OG&E’s upgrades to comply with federal regional haze rules, which the utility unsuccessfully fought all the way to the U.S.