Repeating field entries to new form for easier editing

I have a timesheet form, which has to pull information in from multiple other tables and also run validation as there are finicky rules about what can/can't be claimed. When the end users complete it they are often using up to 20 repeating rows - all using look ups.

The number of lookups and validation involved mean that when you try to edit the entry it falls over as there are too many simultaneous calls to the database (admin-ajax.php errors in particular). As a result the update button never un-grays so edits cannot be saved. Limiting the number of repeats will cause lots of frustration for end users so I thought that if instead I created standalone entries in a second form for each repeating row it would be possible to just edit one entry at a time, with less load on the server as a result.

I have seen how I can use the API to create new entries in a second form with repeating field sections in both forms. However, I would like to use entries from the repeating section sub form in form A to populate standard fields in form B (with an entry in form B for each repeating field entry in form A).

If anyone has done anything similar I would love to know about it. Or, if you've found a way to just edit one repeating field entry rather than all of them...

Thank you!

Lisa