I've not had a chance to test this, but I think in theory, you could add some code like:
If Len(Me.TextBox) >1500 Then
Me.TextBox = Left(Me.TextBox, 1500)
MsgBox "You cannot enter any more data here"
End If
to maybe the OnChange or OnKeyPress event of the text box, I'm not sure if it will work, but it's an approach that might be worth a try, although the code will be executed on each keypress in that text box, so it might make typing a bit painful.
Mike