I am still having issues with the 4.15.3 version of the tool. I am able to get all the materials and models over, but importing the .bsp still causes it to crash.
I don't have access to my code archive at the moment, so I can't really check with an actual 4.15 build, but my guess is it's got something to do with the displacements?
(Also, this is a decompile, and decompiles are technically not supported. Maybe try opening it in HammUEr and saving it back to clean up whatever the decompiler did?)