fzf-preview.vim VS impatient.nvim

You could use impatient.nvim or the new vim.loader module if you’re on nightly. Both work really well. I used impatient for a long time and it reduced my startup time by half. I’m using vim.loader now and it reduces it by about the same amount

The 20-30 ms promise depends on your hardware. In my case, vanilla Neovim takes about 18 ms to startup, so a realistic good startup time for my config is around 50-60 ms. Lines of code isn’t a great reference either because you could just lazy load a bunch of plugins and have more LoC but still better startup times. What I would recommend is using lazy.nvim or if you wanna stick with packer, then pairing it with impatient.nvim .

automatically caches all startup code before :h VimEnter or :h BufReadPre (basically what impatient.nvim does)

there is an amazing plugin called impatient.nvim that cache a lot of stuff and make other pluggins go so fast !

Try installing https://github.com/lewis6991/impatient.nvim first.

:lua vim.pretty_print(vim.mpack.decode(vim.mpack.encode({some = { thing = false }}))) used by impatient.nvim

Did you defined your [[ and ]] mappings in that file or just created it? the after directory runs at the end of your config so you can override this kind of settings. Maybe you are using impatient.nvim? From their README:

Are you using impatient.nvim? It caches lua modules. My startuptime with 72 plugins (including it) and zero lazy loading is 600ms.