YAOUNDE (Reuters) - The governor of the central bank of the six-nation Central African CEMAC zone on Wednesday trimmed its 2015 economic growth forecast to 4.2 percent from 5 percent. Lucas Abaga Nchama, governor of the regional bank, known as BEAC, kept the main lending rate unchanged at 2.95 percent. "The (economic) performance will be affected by a less than favourable international environment and a worrying security situation," Nchama said of the zone, which includes Cameroon, Central African Republic, Chad, Republic of Congo, Gabon and Equatorial Guinea.