I can't into music compression.
Like, I will literally die if I compress all that 240p music I download from Youtube and my laptop mic voice overs. *cough* cough*, see that's what the .pak compressor alone did to me.
What format is it all in? .ogg is typically reasonable on file size without raping the sound.
I think UE4 only supported importing wav files directly and that's why I went the lazy route. I *think* UE4 compresses audio to something less massive while packaging it, but I have to say I never looked into it enough to say for sure.