This is what I am trying to do for some time now (few months), but vibe.d code is not so easy to read and debug. So far I have found out that vibe-core seems to not be the main problem (there are still some potentional speed improvment), but it seems the issue is somewhere in vibe-d:http.

There is some work on new version of this package (https://github.com/vibe-d/vibe-http) , so maybe the performance of this new attempt will be better. I am goint to try this new vibe-http, but I am not sure if it is already in usable state.