Some blog post with details:
https://dev.to/adammcquiff/improve-the-performance-of-webstorm-and-other-jetbrains-ides-11bc
Next, we are going to remove IDE latency using an experimental property called zero-latency that was introduced in 2015. Add the following line to your idea.properties file:
editor.zero.latency.typing=true
We’re going to move on to generally optimising the usage of WebStorm by deselecting features that are unnecessary which will in turn reduce software bloat and increase system memory.
Now, let’s change some settings in the Editor preferences.
Within Preferences, go to the Editor tab and select Live Templates. Deselect any templates that you will not be using.
Emmet is a IDE plugin that helps improve HTML and CSS development workflow, but it comes with many options that go unused and waste valuable system memory. To remove unnecessary options, within the Editor tab select Emmet and browse through the options for CSS, JSX and HTML, removing any unused options.
Intentions is a powerful feature of the JetBrains application family, it suggests solutions to problems that it detects on the fly as you write your code. However, by default WebStorm has every option selected with the Intentions preferences window, and it is unlikely that you will use every technology/language listed, so deselect the options that you do not use. To deselect the options, within the Editor tab, select Intentions, and again deselect any non-applicable languages and technologies.