All shown statistics are over the most recent 24 hours.
18k va. 15k seems to be a typical daily variation on a healthy network, is there anything that makes you skeptical that this fluctuations are certainly out of order?
@Flocker mentioned he's using FTLDNS which doesn't care about the log files any longer.
I'm currently at about 13k queries a day on the Pi-hole in my office. This is how my over time graph looks like (please don't try to reverse engineer what are my working hours ):