I am getting somehow much lower parsing times than normally, thats one thing (not sure if this would be the cause with more than one frame preview tough).
This may be caused by different embree settings for IR and production rendering. But usually you get more rays/s when using the production acceleration structure. There are scenes (only few instances, large meshes) which are awfully slow using IR compared to production, so it depends on the scene.
Another would be a really fast animation preview using "fast preview denoise" - is there a way to turn this on when rendering frame sequences? If not this is the reason why. I am getting decent image preview after 10 - 20 seconds, ideal for rough animation.
The "Fast preview denoise" is the same as choosing "NVIDIA GPU AI" in Render Setup -> Scene -> Denoising -> Denoising Mode. So yes, you can use it for a frame sequence.
How a screen recording would do me good here? I cant set it for multiple frames with Corona render?
Yes, you cannot. That's why I wrote "in case of free navigation" (sometimes I use IR + screen recorder + 3D mouse to record the state of a model).
So it seems what remains is that you would like to use IR because of lower parsing times. Would be helpful to see a comparison from one of your scenes regarding parsing + rendering (the "Stats" tab from Corona VFB) for example an HD image with 10 passes respectively with comparable noise/noise level (10 passes IR do not equal 10 passes production regarding quality). I don't expect any large difference if you set production render settings low enough (this is what's happening when starting IR internally as well for a few values).
Good Luck