Welcome!
That sounds somewhat low but not crazy. Don't know what the local terrain is like but here in the suburb I live in we have lots of hills. I have seen as low as 7MPG average when just driving around locally with no interstate. I get 25 to 28 on the interstate depending on speed and terrain. 70 or 75 doesn't seem to matter much 80 is a little bit less but sometimes necessary to keep from getting run over! For diagnostics first check is tire pressure, the OEM tires run 42 PSI if memory is correct. Doesn't help the ride but goes around corners better :-) Second thing to check if alignment. If the front wheels are toed in or out that can hurt mileage. Ive wondered about mine but haven't checked - its only got 11,000 miles on it - a 2016 I bought new a year ago. You know everyone is going to say bicycle person doesn't know about alignment but I align my motorcycles all the time. If the rear wheel is not true to the front wheel they don't turn correctly. A third thing is the gas, if you get real gasoline mileage goes up, with the E10 mileage goes down. A few years ago I was driving every Saturday to see my mom. I would get on the interstate and set the cruse on my Volt at the same speed. I could tell a difference in headwinds but sometimes the mileage was a few MPG different. Rain is bad for mileages well. My plan was to use the TC for trips and hauling stuff but use my Volt for local trips. My son's car broke and he has been driving my Volt while saving for a new car. He has a job and no wife or kids or debt so Im expecting my Volt to return very soon!