Hi Les,

I don't know how to resolve your problem directly. But when I took over as County Recorder for butterflies, I initially put all my records from one recording scheme into one survey. This became unmanageable, so the solution I now use is to create one Survey per year for each recording scheme. I then apply Tags to the survey so they are logically grouped together. This makes it a lot easier to find records, and see what records I have for each site, recorder etc. For example for 2013 I have five surveys covering the different recording schemes.
Using Additional Filters field enables a number of conditions to be applied, so you could generate a few reports covering all records in a particular date range, or survey name, with the aim that report one extracts say 2m records, report two for the next 2m or so records. Thus for 16m records this would require 8 reports to be run, assuming 2m was the maximum you could export at any one time.

Kind regards
Harry

If the issue is not to tie up your database while exporting, why not install a second standalone copy on another machine, backup the original database & restore to the new copy? Then export from the copy, leaving your main  db free for other uses.