This is fixed in the following changelist. It should be a part of 4.15.1, but should also be a trivial integration onto 4.15.
Change: 3309552
UE-42101 [daydream] Black screen with FirstPersonTemplate and 4.15P4
-Fixed creation of the rendertarget to use the msaa level on googlevr. Also clamped the msaa level to the level that opengl reports the hardware supports.
Files:
//UE4/Release-4.15/Engine/Plugins/Runtime/GoogleVR/GoogleVRHMD/Source/GoogleVRHMD/Private/GoogleVRHMDRender.cpp#5