Can't confirm that. I have to work with gitlab with different customers on several independent project teams. No installation feels fast. Memory is >2GB. Also have it here on a machine with 4GB. No page loads under 1 s. And the ajax requests seem to take even longer than a full page reload. Its a pitty you now load almost everything with Ajax and there's no option to turn that off. I often find myself to click a second time on a link because the browser spinner doesn't move and your progress bar is not really where my focus is.
I had been using 5.1 for quite some time before. It wasn't really fast either, but things have gotten much worse with newer versions.