The Collage takes a long time to load.

Collages with large thumbnails or lightbox effects need to load a number of images. If you publish these images at full quality settings then things will run slowly. By choosing a more compressed file type (like JPEG Medium Quality) you can improve performance dramatically. The Output Format setting is in the RapidWeaver Page Info window under the General tab. This can be a good solution for improving the performance of any image-heavy page in RapidWeaver, not just Collage.