An essay with a word count of 1,500 words tends to be one that exceeds four pages (if double spaced). While this may seem like a lot, do not become discouraged. Finding the right topic to discuss will give one ample material to create an essay which would meet the word count needed.
Examining themes within a text typically provides enough textual support to insure a word count can be met. Some of the themes of Orwell's 1984 are the power of "Big Brother," free will, appearance and reality, loyalty and betrayal, and patriotism. What one would need to do is examine how each theme is supported within the text. Be sure to use specific textual examples to support the thesis.
Another way to examine a text is through the characterizations made. When focusing an essay on characters, one must be sure to understand the character based upon both direct and indirect characterizations provided by the author. Here, one could compare and contrast the protagonist and antagonist of the story. What makes them who they are? What details are provided by the author to support the essayist's understanding?
One last suggestion on an essay over Orwell's 1984 would be to examine the historical context of the text. Here, one would examine the time period and how the novel depicts the period. Questions to ask would be: How does the author portray the time period? Is the author's portrayal of the time period accurate? If so, how? If it is not accurate, then why is it not?
I hope this helps. Good luck on the essay.