Warp Stabilizer is culprit in your case. Even a few instances of it can increase project size dramatically. The only useful workflow for Warp Stabilizer in its current state is to apply it to a clip or two and force Pr to render those clips. If you don't want to take a chance on Pr losing its links to the render files, then you should export the rendered clips as lossless intermediate files and replace the clip instances with the rendered clips.
Jeff