Lewis Hamilton and Nico Rosberg drove Mercedes' new W06 hybrid at a brief 'shakedown' test at Silverstone on Thursday.
German Rosberg drove the car first before handing over to Britain's world champion Hamilton.
It completed 19 laps before a blizzard forced the team to stop running and will next appear at the first pre-season test at Jerez from 1-4 February.
Mercedes won 16 of the 19 2014 Formula 1 races as they dominated the season.
Following the test, Mercedes released two photographs of the car, which looks outwardly similar to last year's but has noticeable detail changes in many areas.
The nose is a different shape to satisfy modified safety regulations defining the shape of the front of the car.
And the bodywork appears re-shaped and slimmer in several places, especially behind the cockpit and in front of the rear wheels, as the team seek to enhance the aerodynamics further.
The team are expected to set the pace again in 2015, following upgrades to both chassis and engine.
Red Bull team principal Christian Horner said on Tuesday that "Mercedes are the benchmark, they go in as reigning champions and favourites".
Red Bull's Daniel Ricciardo, who finished third behind Hamilton and Rosberg in the 2014 championship, said this week: "If we can halve the gap, and at least start the season like that, then it is a good start.
"Then we can try to apply a bit of pressure as the season goes on - and try to be perfect. And when they are not perfect, then we can start putting some pressure on them."
Mercedes' rivals are hoping that a relaxing of the ban on in-season engine development to allow limited improvements will give them the chance to catch up with the German company's standard-setting turbo hybrid power-unit.