This guy made a good tutorial about how to make decent looking glass in Unreal 4:
The main issue with large chunks of glass is that the translucent pass currently does not use the screen space reflections, meaning it is completely relying on the pre-baked reflection captures you put in your scene. These reflection captures are a resolution of 128x128, so it can looks very low quality compared to the screen space reflection if the area you cover with it is too large.
A solution for you could be to render a custom texture for a reflection and later apply it in your shader. This is only usefull if you get really close to objects and want thee rosultion to be much highher than the standard reflection captures.