If a soldier denies an article 15, does it automatically go to court martial or would the officiating officer decide that?

I'm not modern anything, but I did command one unit of 1600 people and one smaller unit as a field grade officer. In both units the Sgt Maj, my S-1/legal officer and the offender's OIC would bring me the case being considered. I would hear everything they all had to say about what kind of Marine the individual was. Then we would discuss the infraction and, based upon the seriousness of the problem and the individuals performance I would decide how we were going to handle the situation. If the individual was an habitual offender, had pushed everyone else to the point of exasperation and didn't seem to be the type of individual who had a desire to succeed, I would bring the individual in, explain what the complaint was and offer him or her the opportunity to offer any (I remember this like yesterday) information he had in "defence, mitigation, or extenuation". After hearing that information I would make the decision whether I wanted to continue the Art 15. If I thought the Art 15 would have an impact, I would confirm that he/she was willing to accept the Art 15. If I didn't think the Art 15 was going to make a difference in the serviceman's attitude, I wouldn't even ask if he would accept the 15, but advised him I felt the situation was not appropriate for an Art 15 and was going to start the process of referring him to court martial. My point is, most officers I knew felt the Art15 was an opportunity for someone to screw up without it being a career killer and it was my opportunity to catch a person's attention and demonstrate to the rest of the unit that such conduct would not be accepted without consequence. At the same time, I didn't feel all punishments or decisions had to be equal. The people who were good Marines whose OIC and the SgtMaj felt were worth working with walked out of my office feeling a lot more hope than the habitual offender.

SGT (Join to see) From the Manuals for Courts Martial, Article 15 Nonjudicial Punishement:
"a) Under such regulations as the President may prescribe, and under such additional regulations as may be prescribed by the Secretary concerned, limitations may be placed on the powers granted by this article with respect to the kind and amount of punishment authorized, the categories of commanding officers and warrant officers exercising command authorized to exercise those powers, the applicability of this article to an accused who demands trial by court-martial, and the kinds of courts-martial to which the case may be referred upon such a demand. However, except in the case of a member attached to or embarked in a vessel, punishment may not be imposed upon any member of the armed forces under this article if the member has, before the imposition of such punishment, demanded trial by court-martial in lieu of such punishment. Under similar regulations, rules may be prescribed with respect to the suspension of punishments authorized hereunder. If authorized by regulations of the Secretary concerned, a commanding officer exercising general court-martial jurisdiction or an officer of general or flag rank in command may delegate his powers under this article to a principal assistant."

So the decision is which flavor of Courts martial to dispose of the charges with. Usually for a garden variety Article 15, it could be a Summary Court Martial.

If memory serves, the only options for an SM is to either accept the Article 15 or deny it and request trial by Courts Martial. But, before accepting or denying, the SM should have been given time to speak with Legal.