How to Limit number of files read

I am using this code to list all the directories and files within these directories.

var dir = @"C:\temp\TestDir";

int option = 1;

switch(option)
{
case 1:
{

PrintDirectoryTree(dir, 2, new string[] { "folder3" });

break;
}

public static void PrintDirectoryTree(string directory, int lvl, string[] excludedFolders = null, string lvlSeperator = "")
{
excludedFolders = excludedFolders ?? new string[0];

foreach (string f in Directory.GetFiles(directory))
{
Console.WriteLine(lvlSeperator + Path.GetFileName(f));

}

foreach (string d in Directory.GetDirectories(directory))
{
Console.WriteLine(lvlSeperator + "-" + Path.GetFileName(d));

if (lvl > 0 && Array.IndexOf(excludedFolders, Path.GetFileName(d)) < 0)
{
PrintDirectoryTree(d, lvl - 1, excludedFolders, lvlSeperator + " ");
}
}
}

Some subdirectories may have more than 100 files.
How to list only first 15 files from each subdirectory?