your system is cheating somewhere.
You say your xorg version is 1.17.1, but before you said "ABI xorg-video-abi-15" that means xorg 1.15.
You need if you have xorg-server-lts-vivid to instal the lts-vivid, and remove the lts-wily package.
otherwise you can upgrade to the lts-wily stack but be sure you only have one, and the corresponding virtualbox version installed.
your system is cheating somewhere.
You say your xorg version is 1.17.1, but before you said "ABI xorg-video-abi-15" that means xorg 1.15.
You need if you have xorg-server- lts-vivid to instal the lts-vivid, and remove the lts-wily package.
otherwise you can upgrade to the lts-wily stack but be sure you only have one, and the corresponding virtualbox version installed.