Hello Thibault,
Embedding minified css and javascript may help.
We do not recommend embedding images unless there is a lot of them and they are smaller than 1KB.
In our experience, most often the bottlenecks are the following:
- Slow generation of the HTML document itself on the client side (slow DB query, ...)
- Static assets are loaded from a slow or misconfigured server.
If you post here a link to your document we can do a quick check to see if there is anything obvious.