You'll get it done! Focus on 100 words at a time and the next thing you know you'll have it finished.
When i used to get assignments like these, 2000 words, 5000 words, I use to type all the bullshit I could think off. More than half of it came naturally and the rest with just a little bit of thinking, you should get it done by tonight if u wish
You could just forget about it and have a beer, why not play some CSS? Do the essay later, it'll be ok.
Don't finish the 1500 words. Hand it in with 700 words and just say that you're not as much of a simpleton as the rest of your class that needs 1500 words to complete the assignment.
oh and try to use words like "I am" rather than "I'm" or "due to the fact that" instead of just "due to", etc that way you can get at least few extra words in a sentence to up your count xD