I also have the same laptop: Dell Inspiron 7559. I managed to boot by adding
nouveau.modeset=0 to GRUB's
When you are in the GRUB menu, press E to enter the GRUB editor. Add
nouveau.modeset=0 to the end of the line that starts with
linux. After you've added it, press F10 to boot. Your system should start. After that, go to System Settings > Software & Updates > Additional Drivers and then select the NVIDIA driver. Right now I'm using NVIDIA binary driver- version 367.57 from nvidia-367 (proprietary, tested).
However I also have problems. Firstly, the NVIDIA card consumes a lot of power. My battery life is 2 hours with Linux (because it only uses NVIDIA GTX 960). With Windows I get 6 hours if I use it mildly. If I do
prime-select intel, and try to log off, it gets stuck and I have to reboot it multiple times to make it boot. Sometimes it never boots back so I have to boot in recovery and switch back to NVIDIA by
prime-select nvidia. I have installed all the Dell graphics card drivers and nothing changed - still doesn't boot with Intel selected. However once I managed to boot with Intel and it gave me 6:30 hours of battery life. Something is weird.