I would definitely retake the DAT in this hypothetical situation. It's okay to have one or two low scores (if it's QR or possibly RC or even PAT in some cases) but to have two low science scores and a low PAT score would definitely hurt your chances. Those low science scores may even make them question your high Science GPA.
A 15 on bio is ugly, and an 28 on QR, who cares. I would say that the person unlikely to gain admissions, but that what others said about me. Who knows?