In your System.out.println, you probably want String.join("\n", FullReport) instead.
That said, unless you know for sure your DataInputStream is exactly 15 lines long every time, I'd recommend something different, and that is using an ArrayList, and reading until there's no more data. The ArrayList will let you dynamically size a little easier than pre-defining your array size. But, again, this is useful when the amount of data being received is unknown.
ArrayList<String> FullReport = new ArrayList<String>();
while (network.available() > 0) {
FullReport.add(network.readUTF());
}
for (String Report : FullReport) {
System.out.println(Report);
}
It's of note that System.out.println automatically adds the "\n", so you probably don't need to do that yourself.
Disclaimer: This is untested. There's probably bugs.