Same problem here:
Opened a .dng file that was 22.9 MB (the DNG was converted from a Sony ARW file using Lightroom CC 2015.1, Camera Raw 9.1)
Made no edits in the Develop Persona (simply hit develop)
The Photo Persona information showed: 5504 x 3672px, 20.21MP, RGBA/16 - sRGB IEC61966-2.1
Made no edits in the Photo Persona
Selected “File”, “Save as”
The resulting .afphoto file is 178.4 MB
The same thing happens if I skip the DNG conversion in Lightroom and take the Raw file directly into Affinity Photo.
