At least 15 people were killed and 28 injured in a road accident in Turkey Friday.The mishap occurred in Isparta province, Hurriyet news reported.The bus was carrying a group of workers, mostly women, employed in an apple plantation near Yalvac district, officials said. Many of the injured are in serious condition.According to investigators, the accident is believed to have been caused by brake failure.The bus first crashed into a wall on the roadside before falling into a ditch.