Scrollable external txt problem

I made my own scrollable external text.
A scrollable textfield with an external textfile with the content of the textfield. The external file is called data.txt

At first I thought it worked perfectly. But I discovered a problem later on. When I type a lot of text in the external file data.txt the processor use is excessively high! (over 50 percent).

The problem seems te increase in proportion of the length of the external text file.

If I Use only a little bit of text ther doesn’t seem te be a problem.

What’s wrong with my code?

(I attached the fla file including the data.txt in the zip document)