Hi ste1nar,
[EDIT] It seems I made a mistake while testing. This issue seems to be expected especially when inset shadows are involved. I will need to investigate further though.
[UPDATE] This isn’t an issue. In your 4.12 project you need to build lighting before running your stress test. While testing I didn’t experience a regression in performance. What is causing the tank in performance is the use of inset shadows. This generates a shadow map per object and when copying an object multiple times this will hit performance hard. I would recommend using dynamic lighting and turn off inset shadows for improved performance.
Cheers,