VSCode Flutter Dart slow suggestions

I'm using Visual Studio Code for flutter programming and not using many extensions. I loved the code completion but it's usually too slow. It takes around 1-2 seconds for showing all suggestions. Is there any solution to this problem? Here is my list of installed extensions:

I was told to add this config:

"dart.previewLsp": true,

which would put the plug-in into speaking the Language Server Protocol rather than a proprietary protocol, and it seems to have sped things up.