Increase the bucketsize to 32 and the number of threads to the number of processes in your machine (dual 2, quad 4)
For draft you can lower the samples for IDL.

A blur of 8 for shadows slows things down, for draft you might want to lower that.

There is one other thing which slows down the render quite dramatically: transparency - especially multi-layered transparency.  So a light in a transparent bulb in a transparent encasing will be slow. But I am not sure how you might work around that.