The 2015 Leaf has the best battery made by Nissan. You need LeafSpy and a compatible ODBII diagnostic port reader to determine actual battery capacity, but a car showing a full 12 capacity "bars" (the little ones next to the charge level bars) and that hasn't been tampered with to hide capacity loss, should be able to go at least 60 miles on the highway at 60MPH, more at lower speeds in mild weather. That number depends on many factors, especially speed and if the climate control is off, providing A/C, or providing heat. It also depends on whether the car is an S, with its power-sucking heater, or an SV/SL with a better heat pump-assisted system.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.