AD 2015 was in the 21st century
2015 is part of the 21st century.
The 21st century AD.
2015 is the 15th year of the 21st century.
The 1st century AD.
It is the first century AD.
1st century AD
The 1st century AD.
It is the 18th century AD.
The first century AD.
The 1st century AD.
It is the first century AD.
It is the second century AD.
The 3rd Century AD.