RNM: unsure how much capacity is actually available. I believe the 2012 bike BMS will shut off at 3.2 volts, which is around 97% DOD at 1C discharge for the farasis cells. The real available capacity is probably 92-95% of rated.
The 2013 Zero S 8.5 curb weight is listed as 355 lbs. The 2014 Zero S 8.5 curb weight is listed as 367, and the 2015 Zero S 9.4 curb weight is listed as 376, so the bike is getting heavier each year.
2014 S uses a beefier frame (19.5 lbs -> 22 lbs), beefier front forks and I think a purpose-built charger.
2015 S has standard ABS, upgraded forks shocks and tires, in addition to the higher capacity cells. Total cell weight for 2014 ZF8.5 is 40.7 kg = 90 lb; given the other upgrades and assuming Zero's weight specifications are accurate, it's likely the 27 Ah cells are slightly denser.
Comparing all the way back to 2012 S ZF9, the 2015 S ZF9.4 has piled on 36 more pounds. All else equal, I'd prefer a lighter vehicle, but it goes to good use here. The 2015 bike has about 20% more range in mixed riding and is twice as quick to accelerate to 60 mph.