I have Kontakt 8 and Komplete 15 but can't find lo-fi Vibes in my Native Access. Watching videos it seems like it should be available to me.
Look at Kontakt 8 Included sounds and scroll down the long page. Together with Piano Uno, it is installed with Kontakt 8 installation, and not listed as a separate product in Native Access.
If you are on a Mac computer, it is installed in "/Library/Application Support/Native Instruments/Kontakt 8/Content/".
My Komplete 15 is the Standard ver.
Lo-Fi Vibes does not show as a separate item in my Native Access either. It is a Leap expansion for Kontakt 8 and possibly then the Kontakt 8 full version is supposed to install it as part of the Kontakt 8 installation. Try opening Kontakt 8 and check Leap expansions available :
