Comment 8 for bug 1381175

I confirm that the problem exists also on a updated install from Utopic to Vivid 15.04, but Nouveau driver is working just fine.

To use Nouveau driver I did the following:
sudo apt-get remove --purge nvidia-settings nvidia-349 nvidia-prime nvidia-opencl-icd-349
sudo add-apt-repository ppa:xorg-edgers/ppa
sudo apt-get update
sudo aptitude install xserver-xorg-video-nouveau

System Info: Ubuntu 15.04
Linux 3.19.0-15-generic #15-Ubuntu SMP Thu Apr 16 23:32:37 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

Nvidia Card: GK208M [GeForce GT 740M]

lspci | egrep "VGA|3D"
00:02.0 VGA compatible controller: Intel Corporation 4th Gen Core Processor Integrated Graphics Controller (rev 06)
01:00.0 3D controller: NVIDIA Corporation GK208M [GeForce GT 740M] (rev a1)

dmesg | grep vgaarb
[ 0.439245] vgaarb: setting as boot device: PCI:0000:00:02.0
[ 0.439247] vgaarb: device added: PCI:0000:00:02.0,decodes=io+mem,owns=io+mem,locks=none
[ 0.439249] vgaarb: loaded
[ 0.439251] vgaarb: bridge control possible 0000:00:02.0
[ 1.336800] vgaarb: device changed decodes: PCI:0000:00:02.0,olddecodes=io+mem,decodes=io+mem:owns=io+mem
[ 29.226146] vgaarb: this pci device is not a vga device
[ 29.599365] vgaarb: this pci device is not a vga device