Toto Wolff says that Mercedes must make even more progress in 2016 as it expects a challenge from Ferrari, following an 'amazing' development curve from its Italian rivals.
Mercedes had dominated in Formula 1 since power units were introduced at the start of 2014 but Ferrari moved from fourth to second across the two years, claiming three wins in 2015.
"I am very pleased with the season," he said. "We've achieved some amazing records this year with the number of pole positions, front row lockouts, race wins and one-two finishes.
"But that's not what's most important. The most important thing is the spirit in the team, which has been fantastic. It's a pleasure to work with these guys and girls and I know they're all as determined as I am to carry this form into next year.
"Ferrari made a huge step forwards last winter and their development curve has been quite amazing.
"We need to be prepared for the same this year also and make sure we progress even further. When you start to think this is an easy ride you will lose."