(AP/Andrew Harnik)

Americans who bought the least expensive versions of the most popular tier of insurance sold through HealthCare.gov will face premium increases averaging 15 percent next year unless they switch to a different health plan, according to a new analysis.

The analysis shows that premiums are escalating for 2016 in virtually all of these plans. And in nearly three-fourths of the counties where consumers can buy coverage through the federal insurance exchange, the plan that was the lowest-price option for 2015 will no longer have the least expensive premium next year.

The findings by the Kaiser Family Foundation, a nonpartisan health policy organization, reinforce a message that the Obama administration has been spreading since the Nov. 1 start of the third year's enrollment period under the Affordable Care Act: Consumers risk insurance-premium sticker shock unless they are willing to switch to a different plan.

[HHS urges: Shop for better plan prices]

The Kaiser analysis makes that point by focusing on the most commonly bought plans within the "silver" level of coverage. In the ACA system, each of four tiers is named for a different metal and is designed to cover a different proportion of a patient's medical services.

Silver is the second-lowest tier, and roughly two-thirds of the people who bought insurance through the enrollment website for the federal insurance marketplace chose a plan at that level. Of those, nearly half chose the plan available in their area with the lowest premiums -- the plans that Kaiser studied in the three dozen states relying on HealthCare.gov.

Cynthia Cox, Kaiser's associate director for the study of health reform and private insurance, said the findings indicate that existing health plans are raising their premiums for 2016, while new ones are joining the markets at lower prices.

In examining premiums charged to a 40-year-old buying individual coverage, Kaiser found that a person willing to switch to the new least-expensive silver plan in his or her area will save an average $322 during 2016. The potential savings exceed $500 in nearly 400 counties and $1,000 in a few dozen places.

Late last month, Health and Human Services Secretary Sylvia Mathews Burwell released a similar analysis based on a different group of ACA plans."“Our message to returning marketplace customers is simple: Shopping may save you money,” Burwell said.

The pushes from Kaiser and HHS are intended to counteract the tendency of most people with health insurance to ignore the annual opportunity to change their coverage. In 2014, HHS announced first that HealthCare.gov would have a convenient feature allowing consumers to "auto-enroll" without returning to the site to renew their insurance. But as last year's enrollment season neared, federal health officials began to encourage people to take an active role in choosing coverage because most could save money that way.

Last year, about half of the people who renewed coverage in the federal exchange returned to HealthCare.gov to comparison shop. About one in three selected a different health plan.

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