How many documents have been indexed with one Lucy index?

[Bill Taylor]

I have used the Java version of Lucene to index a few hundred  
documents.  I have a sponsor who is interested in indexing libraries  
of a million or more documents.  I have been told that Lucene has  
been used for an index of about 15 M documents.  How big is the  
biggest index that has been created with Lucy?

Thank you.
Bill Taylor