Optimus, random freeze without nomodeset, no backlight support with nomodeset

I recently had at work an HP zbook 15 G3 (dual graphic cards: Intel integrated and Nvidia Quadro) I had first Ubuntu with Plasma desktop installed by the lab (worked OK except with second screen and docking station), which I decided to replace by OpenSUSE Leap 42.1, with Plasma too. First I could not install without passing the nomodeset option to the kernel. With nomodeset, the installation went fine, and when I rebooted, I saw that I had no way to control screen brightness/backlight, which was at a painful maximum. Not with the applet, nor with the Fn keys. The /sys/class/backlight was empty. I decided to go on and install bumblebee with Nvidia proprietary drivers. (blacklisted nouveau, mkinitrd, etc). So far no problems, bumblebee worked fine, but still no backlight control. The /sys/class/backlight was empty. If I removed the nomodeset from the kernel options, (keeping nouveau.modeset=0 and nouveau in the blacklist), then I would see intel_backlight in /sys/class/backlight, and could control backlight from the applet. I discovered later that the module i915 is needed for this to happen (I tried to see with i915.modeset=0/1) Nevertheless, after 3 to 15 minutes maximum, the desktop would randomly freeze: the mouse would stutter twice, then everything would freeze: no mouse or keyboard control, and I had to reset with power button. There was the same behavior with nouveau without bumblebee: as soon as I remove nomodeset, the crash is bound to happen. I have a temporary workaround now, where I disable integrated graphics in the BIOS, and installed the binary driver from the Nvidia website, while still booting with the nomodeset option. /sys/class/backlight now contains acpi_video0, and control works only through the applet. There is no error in xorg log, nor in journalctl, except spamming "kscreen: Primary output changed from blablabla", which still happens now. I'm at loss to find the culprit, especially because it worked in Ubuntu. How can I find which modeset doesn't please my configuration? I would really appreciate the Optimus technology for battery life and heat.