The Coral Beauty is one of the hardiest of the dwarf angels but is not recommended as a beginner fish, it requires a mature tank that has stabilized, it is very sensitive to sudden changes in water chemistry and IMHO a 15gal is too small and susceptible {I think that's how you spell it

} to sudden changes. I believe the minimum tank size for a Dwarf Angel is 30gal with plenty of LR for him to graze on.