Elements of Group 16 have lower ionization enthalpy values compared to those of Group 15 in the corresponding periods
The Group 13 elements are all metals
All the elements in Group 17 are gases
For Group 15 elements, the stability of +5 oxidation state increases down the group
Group 16 elements have less IP than Group 15 element due to half-filled configurations of Group 15 elements. This half filled electronic configuration gives extra stability to group 15 element and due to which their ionization enthalpy increases.