This is my list.
Matthew 10:2 The names of the twelve apostles are these: first, Simon, who is called Peter, and Andrew his brother; James the son of Zebedee, and John his brother; 3 Philip and Bartholomew; Thomas and Matthew the tax collector; James the son of Alphaeus, and Thaddaeus; 4 Simon the Zealot, and Judas Iscariot, who betrayed him.
Acts 1:26 And they cast lots for them, and the lot fell on Matthias, and he was numbered with the eleven apostles.
Romans 1:1 Paul, a servant of Christ Jesus, called to be an apostle, set apart for the gospel of God,
Heb 3:1 Therefore, holy brothers, you who share in a heavenly calling, consider Jesus, the apostle and high priest of our confession,
I believe that is a total of 15.