This is a bit strange. I have Company setup to do the same thing and use it with Rust Analyzer and I have not experienced any stuttering at all!

I read down a bit and it seems like someone has mentioned building with "--with json", and this should be what makes the biggest difference here I think! The only thing I can think is that, maybe you didn't have libjansson installed while building Emacs, or it can't find it for some reason. It also needs to be available at runtime!

You can test to see if libjannson parsing is available by running '(json-available-p)' inside Emacs, in IELM for example.

Maybe some of this information will help!