Second (and before you tell you can't I provided SQL Server database support for a PeopleSoft development/support team at a previous employer for five years and I know what is possible if you want to it) consider adding a persisted computed column to the two tables using BINARY_CHECKSUM(<list the 24 columns being joined>). Index this column and join the tables together on this column.

If nothing else, it is worth a shot in a test environment.