'Tis the sad part of Bryce that it doesn't create true booleans, it only renders the results of boolean operations, all of the objects remain. However, Bryce primitives are pretty low RAM intensive... it's only when you do bools on imported meshes that you really start cranking the RAM. Your render times are probably more a factor of texture or material than the boolean-ed objects. Transparent, glass, volumes all eat up render time...