The modeling, detail, and general composition are all excellent, but the lighting needs serious help … and this could well be why it took so long to run.
The problem in my opinion is “classic Cycles.” The light seems to come from everywhere and from nowhere. There’s no drama to the light. Very few shadows. No differences in color. As you see, 90º edges such as the ceiling above the second lamp in image #1 virtually disappear: you had to paint that wall in image #2 but there is no distinction between wall and ceiling again in image #3.
I guess I come from an “old school” of film photography where scenes were carefully lit with light-boxes and strobes, and gels of various hues.
You might wish to experiment with a hybrid technique that has actually worked well for me – compositing renders of the same scene that were built using BI and Cycles.