The average price increased 4.6 percent from $17,700 in 2014.
Used-car sales climbed 5.6 percent last year to a total of 38.3 million.
Certified pre-owned sales hit an all-time high of 2.55 million in 2015.
"The key factor driving all of the trends in used-car sales today is the popularity of leasing, which is bringing younger and higher-quality used cars back to the market," said Jessica Caldwell, Edmunds.com director of industry analysis. "With a record number of lease terminations expected in 2016, for the foreseeable future there certainly will be no shortage of supply to meet the growing demand for used cars."
The price of used trucks and SUVs increased due to falling gas prices, the report found.
"When the price of oil plummeted about halfway through 2015, shoppers returned to the segments that they truly desire: trucks and SUVs," it noted. "As a result, prices of these vehicles increased much more than non-luxury cars. While other barriers to entry dissuade consumers from purchasing these vehicles, gas prices are the primary force that either drown out or ignite the motivation to buy bigger and more capable vehicles."
The report also tracked shopping behaviors and found that certified pre-owned shoppers spend more time researching than all other shoppers, with more than twice as many page views and session durations as either new-car shoppers or non-CPO used-car shoppers.
The heavy influx of lease returns weighed the average age of used vehicles sold down to 4.4 years in 2015 from the previous year's 4.6 years.
Edmunds says: This report is a must-read for any shopper about to hit the used-car lots.