Final answer:
A peak at 15m/z in mass spectroscopy most likely signifies isotope distribution. However, precise identification of the peak also depends on additional contextual information regarding the sample and its mass spectrum.
Step-by-step explanation:
A peak at 15m/z in mass spectroscopy likely indicates isotope distribution. Isotope distribution is observed as peaks on a mass spectrometer's spectrum, which correspond to ions with specific mass-to-charge ratios. The presence of isotopes of a single element results in different peaks because they have different masses. However, without more information about the sample or the context of the peak, it is not feasible to determine the exact nature of the peak since a small peak could be related to a fragment, isotopic peak, background noise, or even a molecular ion peak if the molecular mass of the molecule is very low.