Hi
What about a1 = 15?
Seems a lot of trouble to put this in a cell comment, if that is what
you mean. In a second column you could put the formula
=if(a1<15,"acceptable value","value is greater than or equal to 15")

or you could use conditional formatting, with condition a1<15 to colour
acceptable values.

No need for macros with either of these approaches.

regards
Paul