Hi Dominic, you should be getting a lot more than 14.5 miles, even after a year of use on the old model 30, I am still getting over 20 miles of flat out riding including hills.
Things I would check are –
Voltage when fully charged using a meter across the charge socket pins behind the seat, you should see at least 60v.
Voltage of each individual battery across its terminals, each battery should be at least 12v.
All the battery terminals are tight.
The tyre pressures are at least 30psi.
The wheels spin freely.
If battery voltages are down, speak to Ken as I’m sure there is a 12 month warranty on the batteries.
The batteries do get a little tired after 12 months but should still be giving you a lot more mileage than you are getting.
Range is of course dependant on many factors, how many hills you go up, how much you weigh, headwinds, even cold temperatures affect the range on lead acid batteries.
Hope this helps