A quick update about SteamVR + Index + FS2020 1.15.7 (TL;DR: 
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Insane drop frames # as soon as you open any popup (i.e. ESC), to the point you can recover only in exiting VR mode, closing SteamVR, then re-entering VR mode
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Lower fps on PG areas (ex. Paris)
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Higher RAM usage
It also looks to me the OpenXR Frame Timestamp issue is back from the first FS2020 VR version(s). SteamVR did address this for quite some time, but both the latest SteamVR beta (1.17.x) and the latest SteamVR release (1.16.x) are showing the same problem with the latest FS2020 1.15.7.
In short, the OpenXR API expects a “frame time” which is based on the OS time, but since Windows is using a different epoch than all other OS, this needs to be adjusted. The visible effect of this problem before SteamVR corrected their OXR implementation is that the simulator was displaying frames as if you’d fast forward a movie (skipping frames). It was as if the simulator “tick” was dependent on the OXR “time”?!?!
Weird indeed.