My game automatically updated to 1.6 on Steam, pretty useful feature; however everything I read about this new patch is horrible! What is the point of beta testing if they release 1.6 unfixed?! This is not only irrational but also unacceptable!

I would like to know how to roll back to 1.5. The only mod which I have installed (subscribed) : Dungeon Quest Awareness and I use Skyrim Skyrim 4GB large memory fix. I am afraid of loading any savegame.

Please tell me how to roll back or give me some advice on how to avoid those new bugs

Unnecessary. Skyrim has had LAA enabled since 1.3.10.

Anyways, the only way is to go into offline mode and replace the files with the pre-1.6 files that you have backed up somewhere on your end.

What deaths_soul said, plus:

If you see any issues, try removing the mod you have (It may or may not be compatible). That is really all you can do. (Apart from reading a book or learning to play golf.)

You forget the save game stuff. Things should always be tested on a new game for various reasons if weird things go on in a save file.