The reason it's slow is that you're anchoring the regexp to the end, but you have a other matches in the string which only fail because they don't end at the end of the string.

The obvious answer here is: don't use a regexp. It seems you just want the last four characters in the string that aren't dashes or dots. You could simple remove the dashes and dots from the string, and take the last four characters from the resulting string. (You may need some special handling if the string may contain less than four such characters).