It takes more time because it's doing immense amounts of math to obtain a new effect (new for Poser anyhow): [Global Illumination](http://en.wikipedia.org/wiki/Global_illumination).  If you don't value this effect, you don't have to use the Indirect Lighting features, but keep in mind that IDL makes many old lighting techniques obsolete and can greatly increase the appeal of the rendered output.  If you're happy with adding a bunch of fill lights and screwing around with light settings to get a fairly natural look, great.  Attached was rendered with two point lights.

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