I suspect that it probably is film buildup over the past 6 years. I haven't done anything about the cabin filter yet. I will try the Dawn Advance 3X idea when I remember to buy some.
In general, I have never had any problems with windows in any of my cars these past 40 years and I wonder if there is something different/faulty with the glass produced that year. My neighbour has a 2015 Honda Fit and similar issues. OR else they expect someone to wash their car every week (which I don't). Had a lot of glare on my outside driver's side window the other day too.
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View my fuel log 2015 Micra SV automatic: 7.4 L/100 km ... 38.0 mpg (Imp) ... 13.4 km/L ... 31.6 mpg (US) ...