When open enrollment began on the nation’s healthcare exchanges on November 1, many people who bought insurance for 2015 found that the 2016 plans they had to choose from have narrower networks of hospitals. In addition, premiums might be significantly higher. Insurers have asked the federal government for permission to increase premiums by as much as 40 percent or more. All of this is happening because health insurers say that people who have signed up for coverage under the Affordable Care Act have been sicker than expected.