Advice passing a large parameter

I am creating an RPG function in a service program. This will be called just before calling our shipping application (a separate RPG pgm). The shipping application uses a large, externally defined data structure (roughly 5500 postiions).

All of the information I need for my service program is contained in fields defined in this data structure (about 15 or so of them). But most I do not need.

So my question is this: What is the best practice (most efficient) for the Procedure Interface on my new procedure (function)?

Should I

1. Just define the DS the same and pass it in (it could be CONST)

2. Define only the fields I need (and hope I don't need any additional in the future)

3. Define the PI as pointer and pass the address

Thanks,
Greg