I spoke with Walter directly, and it was simply a miscount.
“Alas, I realized shortly thereafter that I’d miscounted and hence
committed an off-by-one error during the talk: there are 14 (not 15)
type classifications. See the list of primary type category
predicates in clause [meta.unary.cat] in the C++ standard; these
correspond to the classifications established for the core language in
[basic.types].” –WEB
That being said, they are:
template <class T> struct is_void;
template <class T> struct is_null_pointer; //<- arrived in C++11 (std::nullptr_t)
template <class T> struct is_integral;
template <class T> struct is_floating_point;
template <class T> struct is_array;
template <class T> struct is_pointer;
template <class T> struct is_lvalue_reference;
template <class T> struct is_rvalue_reference;
template <class T> struct is_member_object_pointer;
template <class T> struct is_member_function_pointer;
template <class T> struct is_enum;
template <class T> struct is_union;
template <class T> struct is_class;
template <class T> struct is_function;