After upgrade from OG6 to OG7 directly to ver. 2.x: Is there any possibility to use OG migrate (available only in OG 1.5)? I´ve realised that OG Migrate is only in 7.x-1.5 but NOT in OG 2.x.

I´ve accidentally updated my site from D6 to D7 directely to OG 2.x. 

Is there anything I could do to use OG migrate?
For OG 7.x-2.2, the migrate functionality is now coming with the OG module itself. No additional module is needed. Documentation can be found here:

Migrate: Contributed module support: Organic Groups

Which means the functionality is no longer in migrate_og (where it was for OG 6.x-1.x) and also no longer in migrate_extras (where it was, I think, for OG 7.x-1.x).