Passing large amount of data between programs

This is sort of a best practice question.

We have an RPGLE based web service that prices an order. Since we already
had pricing routines that worked off database tables containing order
information we take what comes into the web service and create a QTEMP
version of the tables with the order and run our existing pricing
routines.

This has proven to be fairly slow so we started analysing where. Currently
the largest chunk of time is spent clearing and writing to these tables.
We do build them once per job which makes a difference. We also include
some indexing. Our initial thought is that if we could keep the
information in memory and modify our pricing routine to work off that
memory we could improve the performance. The fallout from this would be
updating our routine that runs off tables to copy the info needed into
memory before pricing and the update the tables afterward. That is to
avoid having two routines that do the same thing. This bit of extra time
on that process is okay.

So, the question is what is the best way to pass that chuck of memory
between programs so that several programs can each update their part?

Brian