How To Reproduce:
1) Create a new project.
2) Enable XR with a Windows Standalone target.
3) Create a script to change XRSettings.eyeTextureResolutionScale at runtime.

Expected Results: The eyeTextureResolutionScale is changed correctly when modified in playmode.
Actual Results: Adjusting eyeTextureResolutionScale fails and results in the error:
"The Requested Render Scale: 0.500000, is too large. Not enough memory to allocate Eye Textures. VRSettings.renderScale reverted to 1.000000.
UnityEngine.XR.XRSettings:set_eyeTextureResolutionScale(Single)"

Reproducible in: 2019.3.0a3 (e289e67be1a5)

Notes: Occurs regardless of stereo rendering mode.