Did you change the entries above in my description? If so, try again with having the values unchanged. My machine is not the best and I could make a playthrough without any problems. Same with Serious Sam 4!

Try to change some ini entries to the following:
texs_ctMaxUnloadsPerFrame = 0
texs_ctTooMuchLoadingTextures = -1
sim_fWorldPrecachingStreamingLoadingDoneThreshold = -1

Sorry but even with this version the fps is still really bad. I haven't tried the one for SS4 but I'm pretty sure the results will be the same.