The suggestion that when there's any error that the scenery isn't stacked correctly or that the user needs to tone down their settings are often the responses to users suggesting that a scenery might have issues or need special attention. While they are truisms sometimes that hides issues with sceneries.
I've around 140 payware sceneries and have problems with a very small set of them. For example Orbx's London City can have framerate issues and you need to be careful what you pair it with. But I have few if any problems.
Now that doesn't suggest that my scenery is layered properly, but I'll give you my procedure for running a flight.
Firstly I use XOrganizer and I'm a big fan of it. It takes a lot of the work out of managing your Xplane set up. So when I plan a flight I firstly use the product to choose the minimum number of plug ins that are needed (so for example if I'm using the IXEG737 I need Gizmo64 or if I'm flying general aviation out of small airports I don't need SAM).
Then to load the scenery I select the flight plan and Xorganizer locates all of the scenery packages along the route. You can then pick and choose which ones you want. So in the case where I had the Vulkan error I chose Tromso (Aerosoft) where I was leaving from, Gatwick (where I was flying to) and the portions of TE UK that were needed. Using the program means that the vast majority of scenery is disabled and the actual scenery.ini doesn't have a lot of structure. I deliberately disable the airports enroute or nearby to avoid loading what I don't need. I have a lot of airports in the Southern England area for example. My thought process is to restrict loading to only what I need. It works for me nearly all of the time in having solid flights.
Now the response will be Xorganizer doesn't work with TE. That might have been true, but no longer is. The developer of Xorganizer and Orbx have worked together so that Xorganizer correctly layers TE. This has been true in the last two versions of XOrganizer. I was also peripherally involved in the work with XOrganizer and Orbx, So how my scenery is stacked is exactly how Orbx and Xorganizer have agreed TE should be placed when in scenery.ini
With the Vulkan error I'm presuming some sort of VRAM issue, but I may be wrong. In the end as I'm simulating flying a commercial jet the stock scenery as I approach Gatwick isn't a huge issue. The documentation for the Inbuilds scenery notes that
'We would ask that you mind peformance (sic). Since Orbx uses extended LODs and higher resolution ortho-imagery, you may have to test around with your graphical settings to get the best balance in performance'
I think that's completely correct. Gatwick plus TE is a big ask on my system and to ensure I complete flights (crashes on arrivals are far more disappointing than those on departure) I may have to pass on using TE with this scenery. I have two options, play around with setting or use the stock UK scenery with Inbuilds EGKK. For me the second seems a better solution and one that I personally have found works.