Marchionne, speaking at a news media conference before the annual Christmas lunch at the team's Fiorano test track, left no doubt that there was a hard road ahead before Ferrari could catch dominant Mercedes.
"We must forget 2014," the Fiat Chrysler chief executive who replaced Luca Di Montezemolo as Ferrari chairman in October 2014. "I don't want to talk about 2014."
TIME NEEDED FOR CHANGE
The Italian outfit won no races through 2014 for the first time since 1993, and has said farewell to two team principals in a general clear-out and restructuring.
Two-times F1 champion Fernando Alonso has left the team and joined McLaren; Red Bull's four-times champion Sebastian Vettel has arrived to try to galvanise the restructured team after it finished fourth overall in the 2014 championship.
Newly team principal Maurizio Arrivabene warned, in his first official news conference, that he could not work miracles and Marchionne agreed the team now needed time.
Marchionne said Ferrari, whose engines in 2014 were out-performed by Mercedes, was paying the price for decisions made under the previous management.
DIFFICULT YEAR AHEAD
"Certain choices and strategies were made by others which, in retrospect, I don't necessarily share," he added. "2015 will be a difficult year that will put the team to a real test."
Asked how long it would take Ferrari to recover, Marchionne said: "I think 2015 is going to be a reconstitution year. It will be Maurizio's first full year with the team. I hope that within 12 months we will remove all the baggage of uncertainty that is going to plague us at least the initial phase of 2015.
"Not to underestimate the significance or the magnitude of the task, I think Ferrari can probably get to the same place (as Mercedes) by the end of 2015. Some of the work has already started. We need to be able to emulate Mercedes’ success."
Arrivabene, who has years of experience of working on the International Automobile Federation’s F1 commission as a sponsor’s representative, said the 2015 car was on schedule and had passed crash tests.
Marchionne said two wins in 2015 would be a success, even if the legion of fans might not see it that way, and three a triumph.
"If we win four, we go to heaven.”