Converting workbook references to R1C1 style to insert into VBA code

I am trying to convert the following workbook reference/formula into an R1C1 reference to put into a macro.

Note: the active/selected cell in this case is C15.

=IF(D15=$D$4, $C$4, "")

The code I have is this:

ActiveCell.FormulaR1C1 = "=IF(RC[+1]=R4C4,R4C3,"")"

Thanks in advance,
Rick