PTWoody said..
... The call on which board is better for downwind is a matter of personal choice in my opinion. 2015 has more volume in the nose but less rocker. Some people prefer that, others like a SIC style with more rocker but less volume.
I have the 2013 Ace (same shape as 2014 although the 2014 has a slightly wider standing area due to thinner side walls at deck level) and I like the idea of my board having a bit less nose volume and a bit more rocker than the 2015 model. I find my board has enough nose volume as it is. More nose volume may make it pearl less when plowing into a wave downwind, but it also means the nose gets blown around more in cross winds. I'd rather have better cross wind performance of the 2013/14 design.
The lower deck on the 2015 would be nice though - for a bit more stability in rough water.
With the 2015 Ace, does the lower deck mean that there's water in the standing area when paddling in flat water? I had that issue with the 2011 version of the Ace called the New back then -VERY deep sunken deck.
I've had 3 versions of the board since 2011 and it remains my favourite board. It's the one constant design I keep, despite switching out a number of other race and downwind boards.