Having first run at a filming day in Bahrain earlier this week, Russell had exclusive use of the car for the opening day of pre-season testing on Wednesday.
Despite ending the day a low-key 12th on the timesheets, 2.765 seconds adrift of the pace-setting Red Bull of Max Verstappen, Russell said that the initial feedback from the car delivered some positive impressions.
Most encouraging of all was the fact that the new W15 has appeared to have got rid of the 'spiteful' rear end nervousness that hurt both him and Lewis Hamilton throughout last season.
Speaking at the end of the day, Russell said: “Overall, the W15 does feel nicer to drive than last year's car. We know that it's not about the feeling, but the speed. Nevertheless, today was about learning and not about chasing performance.
"We're focused on ourselves at this test, and it will only be next week where we see where we stack up against the others.”
With 121 laps under his belt, second only in mileage terms to Verstappen, Russell felt that Mercedes had got itself off to the solid start it needed – especially having elected to run a full race simulation in the evening.
“From hitting the ground, it felt like we had a good foundation to start from,” he added. "We completed lots of laps and have plenty of data to go through tonight.
"We ended the day in a reasonably good spot, and we can build from here over the next two days. We will be focused on maximising mileage for learning rather than chasing an optimum sweet spot with the car.”
Speaking earlier in the day, Mercedes team principal Toto Wolff said that nailing down a better-handling car had been a priority over the winter.
“We had a car that was a handful and difficult to understand sometimes why it was doing what it was doing,” he said.
“I think that has been the emphasis this for this season, to have a stable platform from which we can actually develop onwards. And let's see if we have that.”
