@SparkySven,
Sorry to hear you're having issues. They do seem rather extreme from anything that's been reported thus far.
Yes, the scenery was thoroughly tested on the betas and the latest version is even compiled with SU8, so there should be no issues in-regards to that.
I run Heathrow just fine on a gaming laptop without a hitch (i7, 16 GB RAM and 2070) (although, I have no other third-party scenery add-ons installed), could I perhaps have your system specifications, add-ons list and settings to see if I can make any recommendations for running Heathrow more smoothly. Same from you if possible @maca11.
Cheers.