Comment 27 for bug 1232473

Andris Zāģeris, as per your https://launchpadlibrarian.net/151741411/BootDmesg.txt :
[ 0.927247] [Firmware Bug]: ACPI: BIOS _OSI(Linux) query ignored
...
[ 3.325597] [Firmware Bug]: ACPI(PEGP) defines _DOD but not _DOS

Hence, as per http://www.dell.com/support/drivers/us/en/19/Product/xps-15z an update is available for your BIOS (A12). If you update to this following https://help.ubuntu.com/community/BiosUpdate , does it change anything? If it doesn't, could you please both specify what happened, and just provide the output of the following terminal command:
sudo dmidecode -s bios-version && sudo dmidecode -s bios-release-date

Please note your current BIOS is already in the Bug Description, so posting this on the old BIOS would not be helpful.

For more on BIOS updates and linux, please see https://help.ubuntu.com/community/ReportingBugs#Bug_reporting_etiquette .

Thank you for your understanding.