Whether the Lanthanide series consists of 14 or 15 elements is somewhat debatable.
Lanthanide means "like lanthanum". So strictly speaking lanthanum (La) should not be considered as a Lanthanide. But based on common usage IUPAC acknowledges lanthanum as a Lanthanide. We shall therefore stick to Lanthanide series as having 15 elements from lanthanum(atomic no.57) to lutetium (atomic no.71)