Memory management in editor

My landscape simply disappears in the editor in Play mode. I thought this was simply a setting issue but a quick search shows this is a common memory related problem with many suggested solutions.
A common solution seems to be to Resize>Resample your landscape but when I do I get the following error and the application crashes.

​​​​​​​
So what are the suggested steps to reduce your memory footprint in the editor?

Is it simply the number of assets, textures, texture sizes and texture compression settings?