It is bearable with ',', but I cannot stand it with <space>.
If it is possible to remove completely this lag (not simply reduce it), then it would be awesome.
Perhaps it's a setting you have enabled/disabled, or unrelated to vim?
It is configurable in vim, but then either you have a lag and you are able to use your key sequence, or you don't and <leader> sequences cannot be used.
So maybe I have something configured that sets it wrong, but I do not see how to reconcile both things.
The whole point of Vim’s normal mode is to free up “modifier-free” key mappings for commands rather than inserting characters. So by extension, using “modifier-free” key mappings for commands in insert mode is a Vim anti-pattern (if you want custom mapping’s in insert mode, use mappings for them with modifier keys).
Regarding your issue, I suspect your defining your bindings with the `map` keyword when you should be using `nmap` (or better yet `nnoremap‘).
But yes, these keys' intended functions are actually really damn handy, and I use them on a daily basis.