You dont need a low level to open greens from chests, every chest below soldier has a chance to give you green items, doesnt matter which level you are or which difficulty you play.
Also, like i said in my post, i speedrun screaming bells with handmaiden with specialised gear like double daggers and movement speed on trinket. Still, its just not enough. A run is finished in approximately 5 minutes, 3-4 minutes when lucky with spawns and you get only one chest that has at least one green and one grey in it most of the times. So you basically need 500 minutes to get a little bit more than 100 green dust, which is good for an average of two items. This is not acceptable in the slightest.
I would also like to see an official statement about the exchange system, even so i am pretty sure, that Fatshark is aware of the problem and will fix it, hopefully in the next big update this month.