Paticle Flow rendering with mblur - Building static raycast accelerator takes 2,5H

[PsychoSilence]

I ahve a scene with about 50,000 particle shapes that i need to get rendered with motion blur. without the mblur it takes up to 5 minutes per frame which is fine. With mblur however it stalls calculating...

How can i speed up my renderings and have 3d mblur?