Welcome to Librarium Online!
There's an upcoming tournament at my local hobby store and was just wondering what kind of succes people have had with certain armies in a tournament setting. Do people just go typical necron, throw some CC in there, mass warriors? Just wondering and its 1500 points by the way.
At 1500, I would say that you could choose to have a Monolith (there's where it starts being more reasonable for the price), but definetly have at least 4-5 Destroyers. They are what the priority should be for you, as they can rip apart squads and kill even the strongest tanks all from 3 feet away!
Necrons ~ W 15 / L 0 / D 0
World Eaters ~ W 1 / L 0 / D 0
Dark Angles ~ W 0 / L 0 / D 0
I think that you'll find the answer to your question by taking a look at the Necron Army List subforum. Find 1500 point lists there, and draw your conclusions. If you still have questions, post 'em up.