Long story short: I switched to ubuntu 16.04 with UEFI mode. I booted in UEFI, I created the EFI partition, but after the instalation my BIOS couldn't see ubuntu. I used Boot Repair (with the "try ubuntu without installation" option) and now it works great! But, when the grub menu shows up, I get this EFI/Ubuntu/mmx64.efi option. What is it? If i choose it, my laptop will freeze with a black screen. I should worry about it?
Oh, and another little question (please don't get angry about it) - I'm using a 128Gb SSD for / and 1Tb HDD for /home. I got 25 seconds from the moment I turn on the laptop to the actual desktop environment. With windows 10 (I don't have dual boot) I remember I had under 15 seconds. Again, should I worry about it?