A Miyuki Delica 15/0 measures approximately 1.3 mm in diameter and is slightly lower in height. This is the smallest of the cylindrical Delicas, considerably thinner than the Delica 11/0 (~2 mm).
Yes, and it's even a popular technique with experienced designers. Delica 15/0 is then used to refine borders, create textural gradations or complete areas of detail within a main piece woven in 11/0. The two formats are not interchangeable row by row, but they work very well together.
A 5 g bag of Miyuki Delica 15/0 contains around 1,700 beads.