Its possible caused by a combination of things..
Are the 15 nodes only connected among each other, or is there also a connection to the public network? Are all 15 nodes configured to be in forced Ultrapeer mode?
When no results are returned it could be that both Phex report to be firewalled (status bar icon on lower left).
There is a agreement that search results are limited to 64 by default to prevent flooding on the network. To relax this add a configuration in your phexCorePrefs.properties:
Library.MaxResultsPerQuery = 100
The maximum this setting supports is 255 results.
You must not connect to the public network with a value higher 64. Other servents could ban you.
Are you using the official Phex release or did you build Phex from the latest source out of SVN?
There are a few source tuning you might need for private networks. They are already talked about here in the forums.
I think the most recent one was here:
http://www.gnutellaforums.com/help-s...candidate.html
And an older thread here:
http://www.gnutellaforums.com/genera...e-sharing.html
If you need any more help feel free to ask.