How much difference does 1500 dollars make in my EFC?

I would say that no one will know the answer for sure. Schools can do what they want, so it is conceivable that the question will be used. However, I highly doubt that the question is used in that way. I always viewed the question in the opposite extreme. If you say you can pay $20K and the school determines you can only afford to pay $15K, then perhaps the school assumes you have some source of money, that didn’t show up on the form, and they may offer you less money. I just find it hard to believe that that question is used to make admission decisions.