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?