Yes, sprinkling systems use a ton of water. I have 4 zones of 6 heads at approx 3gpm each that I run twice a day at 8 minutes per zone. So 4 zones x 6 heads x 3gpm x 16 minutes = 1152 gallons per day at my place.
In your case, I would try to figure out the gpm rating of your heads (from the manufacturers website, etc) and then figure out your projected flow from that. I also believe there are flow meters you can put on your main sprinkler line to measure actual usage. From this data, you should be able to compare what you are using to what you should be using. If there's a huge difference, you may have an underground leak. You can probably measure zone by zone to track down a possible problem