Very few people have had the opportunity to review the new Voigtlander 15mm f/4.5 Heliar III for the Sony E-mount but Lenin Ramirez-Sanchez of Moving Electrons is one of the exceptions!
Since he used to own the Rokinon 14mm f/2.8 before switching to the 15mm, much of his review is sprinkled with comparisons between the two lenses. He favours the Voigtlander for a few reasons: it is much smaller and lighter, exhibits less distortion that needs to be corrected in post-production, and communicates the EXIF data to the camera. While the Rokinon has the advantage of an f/2.8 aperture, Lenin states that he’d:
…rather sacrifice those few stops for excellent image quality, portability and building construction.
You can read his full review of the Voigtlander 15mm f/4.5 here!