Mercedes is still way ahead of its Formula One rivals just over two weeks from the start of the 2015 season, according to Toro Rosso team boss Franz Tost.
The German squad dominated the 2014 season, winning 16 of the 19 races, and has looked like the strongest team in the first two of three pre-season tests of 2015.
"I hope the championship will not be decided in the middle of the season, but at the last race of 2015 between different teams - not only the Mercedes drivers.
"Up to now I think Mercedes have run with a lot of fuel in their car - they haven't shown their real performance."
Tost also believes power unit supplier Renault is now stronger compared to last year, especially in terms of reliability, after enjoying a much smoother first couple of tests than last season.
"Renault worked quite hard during the winter months - for example we managed to do 94 laps on the opening day in Barcelona," he added.
"That was a good number and showed the package was already reliable.
"I expect that Renault will make another step forward over the next months - then we will see how close the gap is to Mercedes and Ferrari.
"I think in the end we'll be there. We'll probably have to wait two or three races to get a clearer picture of everything."