So, I am assuming that this a cron job that runs every 15 minutes?
In order to suppress multiple 404 messages, you need to maintain a state of what happened before. The file system is fine for this.

Here is some pseudo code:

if($HTTPCode == SUCCESS)
{
   delete 404Errfile if (-e 404Errfile);
}
elsif  ($HTTPCcode == 404)
{
   print 404_error unless exists 404ErrFile;
   create 404ErrFile;
}
else print $HTTPCcode;
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