Hi Jaye,
A 1.5mm Akoya pearl would most likely be a keshi, with its baroque shape, a by-product of the culturing process.  Seems to me like calling it a "baby" is just a way enhance desirability.  High quality keshi, from mussel or oyster are very desirable.  Exactly how rare is difficult to say.  I'm not aware of Akoya pearls that size with a bead inside.  Please tell us more!