Looking at the metadata, the two photos taken with the 16PM were captured using the 1x main camera (ƒ/1.78 aperture)...and the two photos taken with the 15PM were captured using the 5x telephoto camera (ƒ/2.8 aperture). I'm guessing you probably used the 5x zoom with the 16PM too. If so, we're looking at a 5x digital zoom from the 16PM and a 5x optical zoom from the 15PM. (If you zoomed in even more, say 10x - then we're looking at a 10x digital zoom from the 1x main camera, and a 2x digital zoom from the 5x telephoto camera.)
This is a pretty common issue in low light situations. If the lighting is poor, it'll fall back to the main camera (or even the ultra wide camera) since those let more light in, and then do a digital zoom/crop. There's really not much you can do about it other than adding more light. The stock camera app will choose which lens/sensor it thinks will take the better picture. You can use a 3rd party camera app, such as Halide, to force it to use a certain lens/sensor, but not sure if it would help much in low light situations anyway. The photos may end up being too dark.
