boot - Dual booting Win10 + Ubuntu 15.04

I've installed Ubuntu correctly (in UEFI mode), the only problem I've got now is that it won't load any manager to choose which OS to load at startup.
It goes directly to Windows 10 like nothing happened even though when I keep pressing esc at startup and then i go in in boot order with F9 and choose Ubuntu it loads normally but, as you can imagine, it's not that comfortable.

This is my pastebin from boot-repair that went apparently good: http://paste.ubuntu.com/12649013/

Thanks.

First you have to boot into Windows and disable hibernation and Fast Boot from within there.

To disable hibernation open command prompt as administrator and execute this command:

powercfg /h off  

To disable Fast Boot open Control Panel go to Energy Settings, enable show hidden settings and uncheck Fast Boot. After these steps shutdown the machine (do NOT reboot) completely.

Then reinstall GRUB bootloader to your Ubuntu installation in EFI mode
Boot from the Ubuntu install media - then open a terminal and execute:

sudo mount /dev/sda8 /mnt
sudo mount /dev/sda2 /mnt/boot/efi
for i in /dev /dev/pts /proc /sys /run; do sudo mount -B $i /mnt$i; done
sudo chroot /mnt
grub-install /dev/sda
update-grub  

Now you can choose which operating system you want to boot from the GRUB boot loader menu.

Note :

sda = disk | sda2 = efi partition | sda8 = system partition
disk and partition numbers taken from your pastebin output

To get sure - check the partition numbers, you can easily identify them with GParted.
The (Graphic User Interface) tool is already included in the Ubuntu installation media.