If you're going through the trouble to change a sprocket out for trails, why not go with a bigger change? Your 15/47 to 15/51 is an 8.5% reduction. I'd go for a 12-15% reduction, but that will definitely need a different length chain if you do the rear sprocket.
I run 16/47 on my 2008. Not sure if the transmission gear ratios changed, but I like the taller gearing for the 75mph speed limits in Colorado, Utah, and Wyoming. I have also done some rock crawling with this ratio, with some clutching.
A front sprocket change from 16 to 14 teeth will yield a 14.3% final drive reduction, will require only one smaller part to be carried, and will not change the chain length as much. You could probably get away with not adjusting the chain at all, and just letting it ride a little loose off road, which is a good thing.
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