xpcproxy?

I have no experience with xpcproxy, but I did try to find you some information.
I Googled it and found 8,920 results (0.29 seconds).
https://www.google.com/#q=xpcproxy

It appears to be part of BSD unix and is used in the Apple Systems and was launched under 10.9, but no longer launched in 10.10.
Some info from links:

"xpcproxy(8) BSD System Manager's Manual
NAME xpcproxy -- configures the execution environment for XPC services.
DESCRIPTION xpcproxy is an exec(3) trampoline that configures the environment for an XPC service's execution."

"The XPC proxy is a system component which allows applications to communicate and integrate with each other. An example for this SpringBoard using XPC to display notification center widgets."

I can't say what data is being transmitted by your computer, but what does Little Snitch show when you double click the item in the Little Snitch Network Monitor?
Try reviewing some of the Google links to get more information.