With the same core group of defensive players (KW, MW, MD, Gilmore, McKelvin and Hughes since 2013) this defense in the last 4 years has ranked in pts/game:
2012: 26th (27.2pts/g)
2013: 23rd (24.2pts/g)
2014: 4th (18.1pts/g)
2015: 15th (22.4 pts/g)
How about the following hypothesis: 2014 was an outlier where everything went right and the stars aligned and two players who were playing for contracts had monster years: Hughes and MD.