Been racking my head about this for a while, but as of the past month I'm getting awful performance on all of our web exports. I thought it was just the model I was working on, then I went back and checked all my past uploads and they are running awful too. Tested across a high end PC & a mac. Both my current project and the project from October get only around 2-3FPS at max, where in October the same exact model was easily hitting 30+ FPS in all browsers we tested on.
As is, we can't use this feature at all until it's working, which is a bit of a shame. We prefer web standalones since most of our clients don't have powerful enough PC's to run the EXE standalones (which do run perfectly fine if PC has a GPU), or are mac users.