I tried to render out a complex scene last night with modest IDL settings. It took about 1/2 hour to Precalculate 75% of the picture, until it reached the floor. On the floor I had attached a noise node to the displacement channel. The settings were nothing dramatic, but it took about three hours to precalculate. I am guessing that the displacement slowed down the calculations, and will test that tonight. I may want that detail on the floor in a final render, but I can do without it until the scene is otherwise finished.

LMK

Probably edited for spelling, grammer, punctuation, or typos.