Apple has determined that, in a limited number of older generation 15-inch MacBook Pro units, the battery may overheat and pose a fire safety risk. Affected units were sold primarily between September 2015 and February 2017 and product eligibility is determined by the product serial number.
This is from the page that was just put up on Apple’s support site.
It’s mentioned that customer safety is Apple’s top priority and affected batteries will be replaced free of charge.
To see if you MacBook is eligible for this program, visit the site and enter your 2015 15-inch MacBook Pro’s serial number.