PhpStorm can be very slow in large files as its performing so many inspections. One quick and easy way to speed up PhpStorm is to render using OpenGL. Previously in a 5000 line file it would give the 'eye' symbol in the top right for a long time before changing to a tick (or red/yellow box). After OpenGL it does this almost immediately.
To enable OpenGL:
Then add these two lines below the others: