It's Nasser.
I agree - both are extremely smart when it comes to bodybuilding and smart in general but speak on topics that they are not expert in with the same degree of confidence/intelligence as they do with the bodybuilding topics. When they talk about those issues, they sound like smart people, but not necessarily smart people on that particular topic. Kind of like if a physics undergrad student were to talk about geology - presumably he would come across articulately, but not necessarily correctly.
Also, gh15 and Nasser both share the same opinions on some political issues like recreational drugs. Furthermore, Nasser said in his interviews that he supported Craig Titus, but gh15 felt exactly the opposite. I would say that is Nasser's way of putting the heat off himself, but that will only work for the dim. Those who are a little smarter will look at that as an intentional way to put the heat off the topic of him being gh15, and if anything, would be more evidence to them that the two are one and the same.
Just my opinion. I would guess gh15 is Nasser. Also, Dennis is not as smart as Nasser and I doubt Dennis would be able to write like gh15 does. Few pros could actually, one of them who could being Nasser.