LaTeX is just fundamentally not that fast, especially when pulling in lots of packages. I’m running it on a server with a i7-12700K and 64 GB of RAM, but I didn’t really notice a slowdown when running it on an old laptop, they’re both about the same speed as the official overleaf. With longer or more complex documents, I usually split it into multiple files and edit them on their own, then use include{} to being them into the final file with proper formatting and the right preamble. Of course, thats using a local MikTeX install, so YMMV.
To be honest, I’ve always wondered why you can’t like “pre-compile” a bunch of packages into a binary and include that to speed things up. I’m sure there are good reasons, I just don’t know them.