 Complete the following phrase:  The 2015 FIA World Endurance Championship season was the fourth season of the FIA World Endurance Championship auto racing series, co-organized by the Fédération Internationale de lAutomobile FIA and the Automobile Club de lOuest ACO. The series was open to Le Mans Prototypes and grand tourer-style racing cars meeting four ACO categories. World championship titles were awarded for Le Mans Prototypes drivers and for manufacturers in the LMP1 category, and several World Endurance Cups and Endurance Trophies were also awarded in all four categories. The season began at the Silverstone Circuit in April and ended at the Bahrain International Circuit in November after eight rounds, and included the 83rd running of the 