The warranty transfers with the car. Maintenance does not. There's a $700 fee for that from my local dealers. The answer is easy luckily. Get the 2016. The discount off a 2014 model isn't worth what you're missing from lower mileage of the newer car and the fact that it's a newer car. Check to make sure the 2014 even has the Level 3 charging option which was optional back then. The 2016 will have it standard.
I've seen 2014's for $11,500 so don't get so excited about the $15k price tag you found. The 2016 for $2k more is definitely worth it. If you've narrowed it down to those two cars, the 2016 is the one to get. No doubt.
A fanatic of all things electric. Ridables like electric ice chests and stand up scooters I adore. Drones like DJI, I root for. I'm a fan of both, but nothing beats my love for my 2016 i3 Rex with Deka World. Shhh, don't tell my wife.