Use IF formula based on choice in another cell

I have a drop down choice in (D7) the Choices are "A/B - L/R" OR "N/S - E/W"
In (C15) I have the formula

=IF(B15>0,"Above","Below")

I need to change it to look @ cell (D7) and if they have chosen "A/B - L/R" then the existing formula is correct but if they have selected "N/S - E/W" then I need to use

=IF(B15>0,"North","South")

Thanks for your help