I just voted for deleting a question for the first time.
If I understand that correctly then 15 votes are required to delete a question – and 18 users of this site (probably not all of them active) are capable of voting for deletion.
Is that correct? Has ever a question been deleted by voting? ;-)
The message mentioning "13 votes" referred to the votes I had left on that day, not to the votes required yet to delete the question.