If you are looking for a specific part of that and not the entire set of numbers, you can use $istok.
if ($istok(111.15.57.24,57,46)) { echo -a Match }
The red number is the item you're looking for, and the blue number is the ascii value for a period (the separator used in that number).
If you're looking for the entire thing in a sentence, you can use:
if (111.15.57.24 isin $1-) { echo -a Match }
That assumes you put that into an event that has $1- (such as an on TEXT event).
If you want to check for more a match that ignores part of the number, you can use:
if (*111.*.57.24* iswm $1-) { echo -a Match }
