[silisili]

Sure, just tried it. This is time to open, show the initial contents, then exit. nvim is much faster to cursor around, except when you hit the opening or closing of a json block it hangs a bit, so I'm guessing it has some kind of json plugin built in.

$ time vim tt.json

real 0m5.910s user 0m4.120s sys 0m0.343s

$ time nvim tt.json

real 0m2.894s user 0m1.372s sys 0m0.292s

[nicce]

I did some research and it seems that this particular slowness is due to single line file and if there is some syntax highlighting used with vim/neovim, it reads the line completely to do it correctly.

VSCode reads only the visible content and does not load everything for that line. It tokenizes the first 20k chars of the line at maximum, defined by the "editor.maxTokenizationLineLength" setting.