For batch, you might want to experiment with having the Natural programs use conversational mode - it reduces the overhead a bit. From the Natural programs, use the OPEN CONVERSATION statement, listing the “subprograms” that are to be called via RPC, and the CLOSE CONVERSATION once the batch processing is completed.
With EXS, using conversations reduced elapsed times by a bit more than 5% for batch usage from mainframe to Java RPC. Your mileage may vary 
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