Okay, I decided to uninstall Skyrim after my tesv.exe has disappeared (see previous posting) and do a total clean install.
No mods, no altered ini, no high res package, no saved games, just a complete clean install.
Result:

- still no OA
- striped shadows all over the place
- flat snow surfaces (or any other bright flat surface) are way too bright
- still randomly a huge drop in fps from in- to outdoor scenes

All this issues were non existing with 1.4 version. The fps drop from in- to outdoor did happen in 1.4 but just now and then.
Tried it with previous Nvidia version, same result. So these are really 1.5 bugs