Yes, if your state has credits, definitely consider a new 2015.
Picked up a 2015 Leaf S w/charge package (and some extras like cargo cover) for about $11.5K before sales tax/title/license (incl. fed/state credits/rebates). After tax/title/license, everything inclusive, it was about $14.5K.
MSRP $6K off in dealer discounts, $5K more from NMAC for financing at $0 0%/72 month. $7500 in federal credits (if you pay more than $7500/year in taxes), $2500 in California rebates (not quite as much as Colorado, but still nice).
Out here, used 2013s go for about $12K before sales(use) tax, which would be ~$13.2K, so it just made sense to go new, even though I started out looking at used. Of course, it looks like used prices where you are are a little cheaper, and maybe the tax incentives aren't as good. So used may still be best, but worth looking into!
I think the 2013 had the charger circuitry moved to the engine bay, which freed up a couple feet in the trunk (removed the hump between the suspension columns). 2013 has the heat pump, which is quite a bit more energy efficient unless you're down near freezing temperatures or below. 2013 lets you see the actual battery SOC, which I've heard the 2011-2012 don't let you do (but you could use LeafSpy to monitor). Check whether the 2012 vs the 2013s you're looking at have the same onboard charger (3.3kW vs 6.6kW, quick charge). 2013 supposedly also has some efficiency gains in aerodynamics but it's probably negligible overall. 2013 also should have B-mode, which applies a much higher level of regenerative braking, allowing more use of a "one pedal driving" style.