Duke 390 mileage: My Duke 390 regularly gets 18-20 miles

My Duke 390 regularly gets 18-20 miles per litre on a good long run (if ridden boringly at about 50-55 mph). There are 4.55 litres to an imperial gallon so this works out to about 90 mpg. When I fuel up, my range (2018 Duke 390 ) shows 320km or more. My overall fuel economy has been 3.9l/100km, but that includes most of the KM that were put on by the previous owner. When I reset the trip 1 at fillup it's usually 3.2-3.6l/100km, so I'm getting better economy than the previous owner it seems. I've already ridden my 390 Duke over 1000 miles in my first 2 weeks, I used to ride a bicycle several hours per day and have been riding my 390 as much if not more. I was wondering how many miles can I expect it to last? Should I consider upgrading to another bike sooner if I keep putting this... I ride in Michigan, mostly to and from work--sometimes longer trips. Generally, I have been getting about 14-16 miles per liter, according to the display. This puts the driving range at about 154 - 176 miles. yesterday, I rode to the dealer for my first service. It was 10% highway, 10% city, and 80% two-lane country roads. I rode 143 miles on 2.022 gallons of gas. This equates to 70 mpg. On previous tanks, the least I have gotten is 58 mpg.