You can make an educated guess on when your interview will be scheduled based on last years cut-off numbers. First find the right table: AS, AF or EU.
When your Case Number is below the cut-off number your case is current and you will be notified of your interview via e-mail. Check these tables get an idea, but remember that this is only a guess. DV2015 can turn out very different.
Current means they have enough visa’s available for all remaining Case Numbers, so that’s the best thing that can happen at the end of the years!