I don´t know why, but from one moment to the other sometimes my VRAM usage explodes, from around 5gb to 10 or 11gb in a matter or 1 or 2 seconds. I do have a Geforce 1080Ti with 11Gb VRAM, so when it approaches this threshold, the sim slows down dramatically.
I am flying with the Pipistrel Panthera using default scenery, default clouds and sky and NOAA weather. Below are my X-Plane settings: