$string = "12/01/2015, 10:15: Happy New Year 2015";
if(preg_match('/\d{2}\/\d{2}\/\d{4}\,\ \d{2}:\d{2}:.*/', $string)) {
echo "$string passed check.";
}
Now if you want to ensure that the first part is a valid DateTime format, you can do that too, but it wasn't clear from your request.
Edit: Based on your followup, you could do something like this:
$string = "12/01/2015, 10:15: Happy New Year 2015";
function validate($string)
{
if(preg_match('/\d{2}\/\d{2}\/\d{4}\,\ \d{2}:\d{2}:.*/', $string)) {
$split = preg_split('/:\ /', $string);
$date = str_replace(', ', ':', $split[0]);
$d = DateTime::createFromFormat('m/d/Y:H:i', $date);
return $d && $d->format('m/d/Y:H:i') == $date;
}
return false;
}
var_dump(validate($string));
It just extracts the date section, and verifies that it's a valid DateTime object. I left the preg_match() in because it will ensure that the data coming in is appropriate for the Date validation.