"Updating Objects Flags" taking forever

Upon render, i’m stuck at the stage “Updating Objects Flags”. I couldn’t find any information online as to what this stage of the render is for.

I’m almost positive it has to do with my large particle count (150,000-ish), but have never had this problem with previous scenes with large amounts of particles, including this scene. Previous renders in this scene with significantly more particles (500,000-ish) never even registered on this stage, or at least I never noticed it.

Is there a solution to this problem other than decreasing the particle count? Thanks in advance.

Intel i5-3470 3.2Ghz
Nvidia GTX970
Blender 2.77