It's a shame that XML:DB isn't very active.
It is not shame if people don't use XML databases :)))).
Maybe you could clarify what you mean by handling large files.
When I try to import 5 MB document into Xindice, dbXML and eXist I get OutOfMemoryError or something similar. My myx is able to import large XML and to extract Query using Saxon. myx is simple software - i wrote it for 6 days! I just implemented XML:DB using MySQL, dom4j and Saxon. So, my implementation is "dummy" but seems to be enough stable - yesterday dbxmlGUI worked with it - after 1 hour of debugging. But, on some place dbXMLGUI use DOM - and on that places it still broke! I make one fix for dbXMLGUI to exclude using DOM, and probably there will be more.
I'm not sure about XIndice's implementation but a 15MB document in memory should not be a problem.
For Xindice even 4.6 MB is problem! See Xindice FAQ! And for dom4j and eXist also.
Performance is another issue.
If somebody have some performance testing for XML:DB please let me know for test it with myx. I have seen one, but unfortunatly I don't know where. I will try to find it again, if somebody have some URL or tests, please let me know!