It shall be unlawful for any commodity trading advisor or commodity pool operator, unless registered under this chapter, to make use of the mails or any means or instrumentality of interstate commerce in connection with his business as such commodity trading advisor or commodity pool operator: Provided, That the provisions of this section shall not apply to any commodity trading advisor who, during the course of the preceding twelve months, has not furnished commodity trading advice to more than fifteen persons and who does not hold himself out generally to the public as a commodity trading advisor. The provisions of this section shall not apply to any commodity trading advisor who is a (1) dealer, processor, broker, or seller in cash market transactions of any commodity specifically set forth in section 2(a) of this title prior to October 23, 1974, (or products thereof) or (2) nonprofit, voluntary membership, general farm organization, who provides advice on the sale or purchase of any commodity specifically set forth in section 2(a) of this title prior to October 23, 1974; if the advice by the person described in clause (1) or (2) of this sentence as a commodity trading advisor is solely incidental to the conduct of that person’s business: Provided, That such person shall be subject to proceedings under section 18 of this title.