@Buzzer882, aside from a few specific performance issues that will hopefully be tackled, the other main “regression” is the fact that SU16 switches over to the same world that is used for FS2024. And this has several implications.
1 - FS2020 SU16 will share the same base-scenery problems that currently exist in the FS2024 world
2 - FS2020 SU16 will benefit from the same base-scenery fixes and upgrades when these are made in the FS2024 world
3 - The base scenery that has existed in FS2020 up until now, including in SU15, will no longer be available to fly in once SU16 goes live (depending on whether my wishlist item gets noticed or not).
4 - While some areas of the SU16/FS2024 world have improved, there are other areas where the SU15 world still looks better, sharper, and more realistically coloured than in SU16.
5 - The roads in FS2020 SU15 appear to be vector-generated paths over the top of the base scenery. These appear as sharply delineated paths across the landscape, with moving traffic present. These vector roads do have issues sinking below the terrain in some areas.
6 - The roads in FS2020 SU16 are directly represented by the graphics captured from the Bing aerials. This means they will never visually sink below the terrain. But it also means they are no longer as sharp at low altitudes. And because they appear exactly as you see them in Bing maps, they include static “flattened” vehicles that sit under the moving road traffic generated by FS2020.
7 - The base scenery colours for FS2024 are moderated to a degree by the implementation of “seasons”. Those dynamic colour adjustments do not appear in FS2020 SU16, so the unmodified aerials can have an over-saturated and even “cartoony” look in some areas.
8 - Some of these items are more noticable if your flying style is primarily low-and-slow. Others stand out more at high altiludes.
9 - Whether or not any of these changes in SU16 will be perceived as a “regression” relative to SU15 will vary from individual to individual based on their preferred areas for and styles of flying. Some will and do feel very strongly that SU16 scenery represents a “regression”, others may be neutral on the subject, and yet others may find the new scenery an improvement and upgrade to their FS2020 flying experience.
10 - Once SU16 goes live as-is (without an option to retain the SU15 world) and you only then discover that your preferred area to fly in now looks worse than it did before, there is no going back.