The Question is: "How long would Oceania last?"
It is difficult to question to answer since it is a fictional place.
Research and Responces
One Reason the Soviet Union fell: its populous rose up and revolted and its Military also revolted.
The old and overused phrase: "The bigger they are the harder they fall", comes to mind.
Very Possible in 1984.
Oceania has a very large area and the Inner Party is only 2% of the population.
Many not in the military aren't treated very well, wile the soldiers are treated nicely. They will more than likely find out.
The Soviet's message of Communism didn't stick well.
In Oceania, the message might be implanted, but with how rebellious teens are, it might not stick for long and Oceania will becoming a ticking time bomb of destruction.
Totalitarian states fail because there is always a family or organization that is plotting against them. If they didn't dispose of these groups, they will fail.
The brotherhood is an example.
So basically, from researching about what happened to the Soviet Union, Oceania will not last too long. With its large size, the brotherhood, and the different kinds of treating between the general populous and the military, Oceania is going to fall.