I have the MY 2013 Turbo S. It has quality components, for example:
derailleur is SRAM X0 (10 speed), works like a dream, Magura MT Carbon hydraulic disc brakes are very powerful. Motor is a Go SwissDrive 250W with 342 Wh LiNiMnCoO2 battery. The 2013 also has ANT+ support for, e.g., heart rate belts. The biggest advantage of the new version would be the 691 Wh battery, but because the 2015 Turbo S model has a 500W motor the advantage of the battery size is eaten up by a more power hungry motor. Supposedly a more powerful motor means also more drag from its magnets when riding without power. I think the 250W motor is enough power for achieving 28 mph, so if you can get a MY13 for a good price you could still buy the new 691 Wh battery (~800€?) with the price difference and have nice range. With the 250W motor and 691 Wh battery 50 miles should be achievable in 30% support mode. The new models come also with a 42V/4A charger, so the charging time should be about double (5-6h) compared to the 342 Wh battery. As for estethics, in my opinion the MY13 display and power controller are more nicely integrated than the newer models with joysticks. One of the biggest cons for the MY13 is the lack of chain guide, which at least in my bike results in chain jumping off of the ring constantly when riding hard over bumps etc. But this is solvable by installing a narrow wide chainring.