Refraction on windows is a waist of time. It for the effect to look right there is practically no refraction but it will add hours to your render and make for a very noisy final render. I just use a simple Poser root with transparency and reflect. it renders quick and looks like it should. Bleder Guru talks about this is this video but has a more elaborate node setup. https://www.youtube.com/watch?v=KyXRBu7gn2o&t=5s

W10, Ryzen 5 1600x, 16Gb,RTX2060Super+GTX980, PP11, 11.3.740