I've checked the BBFC site for this release but the information provided there muddies the waters even further.
According to their site, all versions submitted were passed uncut and both 2D and 3D versions of the extended cut were given a rating of 15 on the 9th November, 2015.
Note, however, the different times shown for the versions submitted for classification.
3D extended: 164m 04s (2h 44m 04s)
2D extended: 157m 15s (2h 37m 15s)
According to this, there is a difference of just under 7 mins between the two versions submitted!
I'm unable to explain it but for those wishing to investigate further, here's a link to the relevant page of the BBFC site. Go to the section headed 'Related Work' and click on 'Feature'.
http://www.bbfc.co.uk/releases/hobbit-battle-five-armies-2014