Add " ..." to end of string

Formula:

=IF((LEN(O20)>18),  (LEFT(O20,15) & " …"), O20)

This is basically the idea of what I need done in VBA.

Essentially, I have cells O4 through O34 with text in them. If the text exceeds 18 characters, I want the 3 dots to be placed at the end of the 15th character in the cell. This way at quick glance I can see that there is more text in there, then I can click on it and read the entire text in the function bar above. The problem, obviously, is that I cannot have this formula/function in the same cell as where I will be typing the text. For the above formula, I have it in another cell just to be tested, and it works good. If I can have the same formula/function written in VBA (I think), this would solve that problem.

I have attached the file for reference.

Thanks in advance!