@agentdark45 - Sun in HDR is already aimed through the main doors, just not straight in the middle, it has around 30 degrees offset - you can see it on the soda machine shadow. But I will try that version today :)
@snakebox - I am pretty sure that the plane (portal material) works both ways, no matter of the facing.
@antanas - First of all, thank you very much for you suggestions. Yeah I have a separate portal plane for each window (7 in total on the front doors, but they do not overlap) - it might be wrong :/ so I will try to cover whole doors with one big portal. I am creating portals from the inside maybe a few inches apart from the actual window, so that might be the problem as well. All my glass materials in this scene are already having the "thin" option ticked.
I am open to more suggestions :) it helps a lot! Now back to experimenting!