I tried a couple of environment vars to see if I can fix this with with no success.
PROTON_USE_D9VK=1 may improve things slightly but it crashed on my machine due to Intel Haswell having incomplete Vulkan support.PROTON_NO_ESYNC=1 made the problem considerably worse.PROTON_NO_FSYNC=1 had no noticeable effect.Anything I haven't tried either will not affect load times or isn't applicable to this game. This more than likely seems like an issue with synchronization being really slow.
Edit: I looked into this a bit more and it seems to be doing over 50,000 context switches per second while loading. This is definitely seems to be part of the bottleneck.
PROTON_NO_ESYNC=1`x1 2019-08PROTON_NO_FSYNC=1`x1 2019-08PROTON_USE_D9VK=1`x1 2019-08
First off, thank you very much for your work on Proton, excellent to see Linux support for more games!
SWB2 has a bug which makes loading times before starting a match really long. In single player mode, this means that loading a game goes from 5-10 secs (Windows) to 60-100 secs (Linux). Additionally, this breaks multiplayer mode, because the game times out when trying to join a match, making it impossible to play.
This bug is a long-standing one in Wine, with a report from 2012 here. It appears there is a recent (Jan 2018) patch at the very end of that thread, which I have not tested but according to the comments there seems to fix this issue. Maybe worth looking into adding it to Proton?
Thank you for looking into this!