If you are doing a lot of deletes on rows from a table, consider using MultiLoad rather than BTEQ. MultiLoad completely avoids use of the TJ and is restartable.
To minimize the number of TJ rows being generated on an INSERT . . . SELECT request, consider doing a multistatement INSERT . . . SELECT request into an empty table from both of the other tables. This only puts one entry into the transient journal to let the DBS know that the target table is an empty table and to drop all the rows in the target table if the need for a rollback is encountered. After the new table is created, drop the old table and rename the new table to the name of the old table.
More details on both the delete rows and INSERT . . . SELECT request are available online in the Support Link Knowledge Base.