[Koha] Staging MARC files

Hi all: We've been doing a retrospective conversion project in-house & we've created a file with some 4,200 MARC records (approx. 3-4 mb), using v.3.01.00.002. I'm in the process of trying to stage these records into the reservoir. It's taking a very long time, however, so I'm wondering if folks have any guidelines or rules of thumb about preferred file size / max # of records per file. The most I believe I've staged at one time previously was 54, which went very smoothly. A separate question: When managing staged records, it looks like users have access to just the last 15 batches. Is this correct? Thank you, Cab Vinton, Director Sanbornton Public Library Sanbornton, NH