I upgraded directly. The option appeared as a default option, since I'm not
used to do upgrades using the GUI I accepted its suggestion, the strange
thing for me was not seeing 15.10 as an option. I though that 15.10 was not
supported and I was ok with that.
Before rebooting I installed the system
Public bug reported:
everything was updated to 14.04
several other failures appeared during update
ProblemType: Package
DistroRelease: Ubuntu 15.04
Package: init (not installed)
ProcVersionSignature: Ubuntu 3.19.0-31.36-generic 3.19.8-ckt7
Uname: Linux 3.19.0-31-generic x86_64
ApportVersion: 2.17