Hi Fin,
I'd say 15 miles on setting 3, that's pretty good. Depends on terrain, how much effort you're putting in, wind etc. etc.
Last Sunday I rode about 11 miles, on my Ezee conversion, to a little coastal village. This meant a climb out of my village, a descent into and climb out of another valley and a final descent to the coast. After an excellent fish stew and bottle of beer, I set off to climb out of the village. Only half way up the climb out I was down to one red and one yellow light with about 9 miles to get home. Panicking slightly I had to nurse the battery, turning the power of on flats and descents. The battery recovered some voltage during these off times and I made it home with just the red led showing. Total trip 23 miles and a lot of work from me. My battery is now 2 1/2 years old with 182 charges, all partial. Oh and I always ride on setting 2.
I find the difference between 2 and 3 to be substantial on an ezee, I only use 3 on the steepest hills when I'm feeling my age
So, depends on so much more than just you're weight.
I'd say experiment with lower settings and/or no assist at all on flats and slight descents. You'll get fitter and you're range will increase.
Happy cycling.