I have had no performance issues in Developer Mode prior to SU6. If I edit a large airport that I was editing previously in SU5 (for example KDTW), performance starts out at acceptable levels, even in 4K resolution. As I continue editing (10 minutes+), refreshing of assets, such as taxiway signs becomes slower and slower and eventually the editing/asset refreshing lags 7-10 seconds behind the edit. Reducing the sim’s resolution to 2K, using the Medium global graphic setting and restarting the sim makes no difference. The performance slowdown seems to occur at the same rate. The base VRAM usage in Win 11 is 1.0 GB using an nVidia 4080 Super with 616.56. In the sim, I have DLSS on at 2X and Performance. The sim never reports using more than 8 GB VRAM in Developer Mode. I have 64 GB RAM and a fast Intel CPU.
Is this just a limitation due to the size of the XML file (90,693 lines)?
This has been a problem with the SDK since SU6. The main problem for me is with drawing taxiway points. The lag after a few minutes is quite annoying. Look at this post:
Hopefully is gets fixed soon.
Thanks. How’d I miss that other thread?
@here
The build with the fix candidate will be available very shortly.
Regards,
Sylvain
Thank you so much for your efforts! 
Just curious as to whether the lag problem when placing taxiway points has been fixed. It seems to be performing much better with today’s update. I worked on a project for about 15 minutes and had no performance issues. Unfortunately, though, I’m still having the problem of not being able to rotate a new runway by grabbing the green handle on the end.
Hello @retireddude53
Yes, the patch deployed yesterday is the one addressing the Scenery Editor performance drop among other things.
The fix for object rotation will come with SU7.
Regards,
Sylvain