There are several people in the Bible, whose names consist of 15 letters. One of them is Zaphnathpaaneah. This name actually belonged to Joseph and was given to him by Egyptians. You can find it in the book of Genesis 41:45. Another one is Mahershalalhashbaz, which belonged to a son of the prophet Isaiah. He was born to him by a prophetess and the boy was conceived and named as a sign for Israel. The name means the “robbery is on the way”. You can find it in Isaiah 8:1.