People who buy insurance through Covered California for 2015 are likely to see an average rate increase of 4.2 percent in their health care premiums for 2015, health benefit officials announced Thursday. About 16 percent of consumers could see their rates stay flat or go down. Thirty-five percent could see hikes between zero and 5 percent, while 36 percent could get increases between 5 and 8 percent — and 13 percent of consumers could get a rate increase as high as 8 to 10 percent, executive director…