In addition to 15 companies as per section 275 he can also join other companies listed in section 278.
Section 278
EXCLUSION OF CERTAIN DIRECTORSHIPS FOR THE PURPOSES OF SECTION 275, 276 AND 277.
(1) In calculating, for the purposes of section 275, 276 and 277, the number of companies of which a person may be a director, the following companies shall be excluded, namely :-
(a) a private company which is neither a subsidiary nor a holding company of a public company;
(b) an unlimited company;
(c) an association not carrying on business for profit or which prohibits the payment of a dividend;
(d) a company in which such person is only an alternate director, that is to say, a director who is only qualified to act as such during the absence or incapacity of some other director.