I'm still getting constant disconnects on my second X15. Now the scroll wheel spazzes out as well. I can't confidently play any competitive game because there's a good chance it's going to disconnect right in the middle of a game and the scroll wheel can't be trusted either.
This mouse is a joke. No amount of firmware updates is going to fix poor qaulity faulty wiring.
On both of the X15's that I have, if you wiggle the cable where it comes out of the mouse itself, that's what causes the disconnect.