Just buy it now. There isn't that much difference between textbooks (especially if it's just the difference of one year). I had access to 2011 and 2012 and seriously the only difference was in the wording, some excessive information was cut out in 2012 (e.g. happy planet index or something like that) and one of the chapters in the last topic was quite different - it was about the macroeconomic objects of the year's budget. Even then, this information is out of date (the 2015 textbook gives information about the 2014 budget - when you should be referring to the 2015 budget through news etc). Essentially no real advantage.
Oh and also stats were changed. Still, you can easily find these online! (and more up to date).
Get it early!