Raytracing for hair is always a killer.  If you are using it for a portrait, set if and walk away for a few days.  If the image is smaller in your scene, then take raytracing off the hair.

In cases where scene rendering slows to a crawl, it may be a good idea to split your scene into fore-, mid-, and background and render those separately.  Save the renders as PNG and assemble everything in a 2D program (PSP, Photoshop, GIMP, etc).  PITA but it could save you the trouble of finding low poly substitutes and replacing everything in the scene.  Another alternative, if you have a background cluttered with objects, convert that background into a wallpaper image within Poser.  It would take the load off render time.