Mauricio,
stability wise it is perhaps too early to say for sure, but 2015SP2 hasn't crashed on me yet. And that is with 8 hrs daily use for the past couple weeks. It feels more stable than 2014 to me.
There's a few enhancements and fixes in 2015 that have become indispensable to me - mainly in ICE: the fast tab shortcut (find nodes instantly plus it smart autocompletes queries) and the ICE editing offline mode. That's just two but they make a world of difference to me.
There is actually a sh*tload of new features though, check this
https://area.autodesk.com/userdata/prod ... latest.pdf, I was amazed too. You tend to forget a feature is new after a short while, just assume it was always there. Muting an ICEtree? Couldn't do that before? Really??
Oh, and in SP2 they fixed a few totally annoying things (like the buggy refresh in the curve editor).
So, at least in my opinion, I'd definitely upgrade. YMMV ofcourse, yadayada.
Cheers,
Jasper