וַיִּקָּבְצ֥וּ יְרוּשָׁלִַ֖ם בַּחֹ֣דֶשׁ הַשְּׁלִישִׁ֑י לִשְׁנַ֥ת חֲמֵשׁ־עֶשְׂרֵ֖ה לְמַלְכ֥וּת אָסָֽא׃
So they gathered themselves together at Jerusalem in the third month, in the fifteenth year of the reign of Asa.
Related passages and parallel verses for II Chronicles 15:10.