The f/1.5 lens is useful in low lighting conditions because it lets in more light, but with a wider aperture comes a compromise in image sharpness in certain areas of the photo. Therefore, in conditions where the lighting is better, the f/2.4 lens that's also included will provide a crisper, higher-quality image.
Not quite. The wider f/1.5 aperture will allow very sharp pictures
at the focal plane, and a shallow "depth of field" so that the further from that focal plane the more pleasantly blurred objects appear; the f/2.4 aperture will also offer very sharp pictures at the focal plane (as aperture closes down to values above f/8 or so you start hitting appreciable light diffraction effects which soften the image, but there is no meaningful difference between a well-made f/1.5 and an equally-well-made f/2.4), but the depth of field is moderately larger so objects just a little outside the focal plane are not noticeably blurred. At the same time, an f/2.4 aperture is about 2/3rds of a stop - 1.6x - "slower" than the 1.5 aperture, so shooting with f/2.4 means you are more likely to see motion blur from either your phone or from the subject.
If you are seeing more blurred-subject images coming from an f/1.5 aperture than from an f/2.4 aperture, that is all about technique and can be corrected - take better care in selecting the focal plane and not moving between focus and picture taking. If you are seeing, however, the "eyelashes out of focus while the eyeball is perfectly in focus" (or worse, "the tip of the nose is crystal clear and sharp while the eyes are all blurry") then you have too wide-open of an aperture and stopping down will help. That said, the natural depth of field of an f/1.5 aperture lens on a phone camera is already very deep (around the same as an f/8 or so in a DSLR by my eye, when viewed at full resolution), so the benefit of going "almost a stop smaller" in aperture is not really going to be meaningful in almost all situations. That "natural depth of field" characteristic is due to how smartphone lenses are constructed, prioritizing compactness over "subject separation" image quality measures.
IMHO the "dual aperture" of the Samsung is a gimmick. Instead of providing something that really could solve the problem of limited depth of field (a
variable aperture, using 9+ rounded blades etc, as seen in all modern standalone cameras/lenses but heretofore never seen in a smartphone camera, or something with multiple stops down not just one 2/3rds stop down) they provided a cheap and easy gimmick that doesn't really do what they claim to the extent they claim it, and you see a bunch of malinformed parroting of Samsung talking points out there as a result.
