I would tend to agree on paper.
Still, I don't know why, but Sion 2015 is the most played concert on my playlist. I don't know if it is emotional because it is the last I saw, the sound quality or the performance... TR is definitely slower than in 2005, yet it is very warm, clear, well balanced even with the karaoke mode, and I'm not sure it is "worse" than in 2005. Just different, maybe for the best. SOS, SAN, HFB, GH, YLT are very good on this gig. And I find BIA in 2015, albeit not played very often, the best since 1985: flute intro, synth, faster than in 1996/2001, retaking the good old Les Paul...and KOG in Paris was amazing.
I quite don't understand why so many people think 2015 was a bad year. Different, slower than early years, but clearer, more emotional. A good year to me !