Bryce is just gonna be slow. You can't fix that. Like it was said above, u get what u pay for. I use 3dsmax 4, wich costs upwards of 1000$ to render. It goes about 4x as fast on the same system. A good solution if u have a big lump of money around is to buy something with a better rendering engine than bryce, and just export and import ur scenes. At least its alot faster than RD.