• For fun, here is an alternative

    😎

    USE tempdb;

    GO

    SET NOCOUNT ON;

    DECLARE @STR_DATE VARCHAR(6) = '083115';

    SELECT CONVERT(DATETIME,STUFF(STUFF(@STR_DATE,3,0,'/'),6,0,'/'),1);

    Output

    2015-08-31 00:00:00.000