Mercedes driver Lewis Hamilton said the W15 is a clear improvement over the previous iteration.
The British driver finished third during the second day of pre-season testing at the Bahrain International Circuit after completing 123 laps.
He said it was a “productive day,” and that the team “gathered lots of learnings about the W15, both in our long running and single lap work.
“We’ve clearly made an improvement with this year’s car and it’s much nicer to drive.”
Hamilton will leave Mercedes for Ferrari at the end of the season, replacing outgoing Carlos Sainz and teaming up with Charles Leclerc. However, his commitment to the Silver Arrows remains intact until the time to say goodbye arrives.
“A big thank you to everyone at Brackley and Brixworth for the efforts they’ve put in to deliver that over the past year,” he said. “I’m really grateful for all their hard work.
“We’ve still got progress to make, of course. But this is a good foundation for us to build on.
“We’ll keep our heads down and continue to work to find improvements, both over the rest of the test and into next week.
“I’m looking forward to being back in the car tomorrow morning and continuing that learning.”