Within 15 days after service upon the respondent of the notice, the respondent may file with the Commission a notice of defense in which the respondent may:
1. Request a hearing;
2. Admit the accusation in whole or in part;
3. Present new matter or explanations by way of defense; and
4. State any legal objections to the complaint.
Ê Within the time specified respondent may file one or more notices of defense upon any or all of the above grounds, but all such notices shall be filed within the period specified above unless the Commission authorizes the filing of a later notice.