I didn't think it was 15...here's what I found at a website:
Everyone knows that Moses was the leader of his people and that the Lord had instructed him to climb Mount Sinai where he received the ten commandments. Most people believe that the commandments that Moses recited to his people and which are listed in Exodus Chapter 20 are the ten commandments that were written on the stone tablets that Moses broke but this is not so. These commandments were never written by the Lord or inscribed on stone tablets as is commonly thought. The Lord spoke these commandments to Moses who then recited them to his people.
It was at a later time when he had ascended Mout Sinai that the Lord gave Moses two tablets of stone on which the Lord had written the ten commandments by hand (Exod 31-18). Even though God had told him before descending the mountain that his people were worshiping a golden calf (Exod.32;7-8), when he actually saw them he purposely destroyed the most sacred and precious things ever given to mankind before anyone else had a chance to see them. We know exactly what was written on the first set of tablets because in Exodus 34:1 the Lord said to Moses, "Cut two tables of stone like the first; and I will write upon the tables the words that were on the first tables, which you broke". Thus it was that the second set of tablets contained exactly the same words as the first set of tablets. These tablets were then placed in the Ark of the Covenant for safe keeping. Since Moses did not recite the commandments that were written on the first or second set of tablets, the people continued to believe that the commandments that he had recited originally were the ten commandments. To this day, most people do not realize that the commandments in Exodus Chapter 20 were never written on the stone tablets but were only recited by Moses. God's ten commandments, as written on both the first and second sets of tablets, can be found in Exodus Chapter 34.