Experience with iPad2s running iOS9 and UE4.16 or later

We have an educational game using Google VR (hence needing 4.16.3 or better) that runs fine on test machines, but runs slowly, with no textures on an iPad2 running iOS9. The slowness is to be expected, but the lack of textures is a surprise. Is this a RAM issue - these are bare minimum tablets, as schools can’t really afford top of the line machines - or optimisation of the levels that is needed?