What do you mean 2015? He's still releasing new stuff and forums are still exploding over it. :D
Most recently he posted a part of the epilogue on snapchat and archived it here: http://mspfanventures.com/?s=17075&p=1
That was the "credits" rather than the epilogue, but you can see it in full on the official site if you haven't already:
http://www.mspaintadventures.com/?s=6&p=010029
"2007-2015" is weird because it started in 2009 and it's looking like the epilogue will come in 2017. We had [S] Collide and [S] Act 7 in 2016 so the webcomic itself definitely didn't end in 2015. It may be that they're referring to the famdom, as Jailbreak started in 2007 and the famdom died down significantly from all the pausing before the webcomic itself finished.
the things on snapchat (after the part on the website?) are mostly by "Cohen Edenfield" rather than by the author of homestuck (Andrew Hussie), but there are continuing to be some things posted there. But not by Andrew.
1) 800,000 words plus pictures & videos
2) an internet-induced psychosis spanning 2007-2015