Reminder Worksheet

I have got a workbook were I register our personnel.
In one sheet I have listed all our personnel and the dates their contracts expire.

Now this is what I am looking for:

Between 15 days and zero daysbefore someone's contract expires I want a pop-up telling me so. The person's name has to be in the pop-up.

I already got this


Private Sub Workbook_Open()
Dim c As Range
For Each c In Range("E2:E126")
If c > -15 And c < 0 Then MsgBox c.Offset(, -3), vbOKOnly + vbInformation, "LET OP! Einddatum contract nadert!"
Next
End Sub

I want the pop-up only when I open the workbook(not everytime I change something in the workbook)

In the workbook are more sheets, the code I have only works with one sheet.