Over the past month the 2015 trend line has been dropping faster than all other years before 2010, and so, as of the end of May, 2015 has less ice volume-wise than all the other years preceding the post-2010 era. Going from 399 km3 more ice than 2007, for instance, at the end of April, to 395 km3 less ice now.
On the other hand, big droppers like 2010 and 2012 have increased their lead over this second rebound year, and the latter now has almost 2000 km3 less ice than 2015, just like 2011. The difference with 2013 has gone down 240 km3 to 998 km3 more ice now, and the difference with 2014 has increased with 82 km3 to 1208 km3.
All the differences are more clearly visible on Wipneus' PIOMAS volume graph:
All of this doesn't come as a surprise. Despite the early attack on the multi-year ice in the Beaufort and Chukchi Seas (see ASI 2015 update 1), much of the Arctic was pretty cold for much of May (see for instance the DMI 80N temp graph).
Based on gridded data, Wipneus produced this great map showing the difference with last month, red being the areas where ice has grown or thinned less: