I got it to lag really badly a couple of days ago where I was just sitting waiting for it to complete words. Had to restart, but other than that one time it has felt fine.
It could be some extension, I have had vs code lag really badly in the past (almost a year ago) when I was using the java support extension by Red Hat, I have even had JVM crash while using that configuration. Now I have only a few extensions enabled at a time based on the workspace and do not have performance problems. I have also switched to NetBeans for java development since Apache has taken stewardship of the project. It is a really great and under appreciated IDE :)