Also, to expand on adp's answer...

LuxRender is an unbiased renderer and therefore, for the present time, is much slower than Poser's firefly. What might take a half hour in Poser will take hours and hours in Luxrender. The result however will be vastly superior in LuxRender. If you aren't prepared to waive time for a better render then LuxRender may not be for you ;o).

The LuxRender programmers are busy getting GPU rendering to work with it, which will speed it up a lot if you have a decent graphics card, but for now, it's all CPU and is slow.

Laurie