Any solution to open material editor without opening the engine, my pc is kind of dated and larger materials, like landscapes are taking too long to preview with the editor open too.
As far as I know there is no way to just open the material editor. But when you want to do fast + realtime changes, you can use parameters in your material and then create material instance constants 
Also make sure to set the quality settings to low so that the engine will run faster
You can turn realtime off in a viewport so that it only updates when you click or drag in the viewport. Try turning realtime off in the level editor, that may give you a better experience while working in a sub editor.
Cheers,
Michael Noland