DB Design :: Convert Integer Date (MMDDYY) And Integer Time (HHMMSS) To DateTime Format?

Working on a new database where the Date and Time are stored in a Date Time Field.

Then working on an OLDER database file within the same SQL Database contains these 2 items as integers:

transDate = "71615" (July 16, 2015)
transTime = "12345" (01:23:45 AM)

How do we convert both of them into a single SQL DateTime field such as "2015-07-16 01:23:45.000" so that it can be used in a join restricting to a date time in a different SQL File that properly has the DateTime in it?

This works well for converting the transDate Part in the select statement:

   dbo.IntegerToDate(at.transDate) as transDate

   * That returns: "2015-07-16 00:00:00.000"

* The resulting data must work directly in a Microsoft SQL Server Management Studio Query using either using the "on" statement or part of the "where" clause. In other words, NOT as a stored procedure!

Also must be able to be used as a date difference calculation when comparing the 2 files Within say + or - 5 seconds.