C9 being the group size, these are the formulas I used:
=IFS(C9<5, "0%",C9>=5,"15%", C9>=15, "25%", C9>=40, "40%")=IF(C9<5,"0%",IF(C9>=5,"15%",IF(C9>=15,"25%",IF(C9>=40, "40%"))))
C9 = 43 but the result of both calculations is still showing 15% instead of 40.