If a Mugen 5 or FS140 or TS140 with fan replacements can compete with the D15, why even consider the D15? Its more than 2x as expensive.
I often wonder why myself. Frost Spirit 140, TRUE Spirit 140 Power, Le Grand Macho RT all compete or beat D15 with stock fans.
I agree, no reason to pay more money for same cooling. But people do.
I ended up getting D15S over any other cooler for a few reason and also what
@ciarlatano mentioned
It has best front RAM, back RAM/VRM clearance (technically Le Grand Macho RT has better front RAM, but not back clearance), It has better height clearance than most others especially Spirit 140 Power (what am I gonna do with a 171mm cooler ?, when almost half of the new cases I'm looking at to get in the future are ~160mm, also horrible width for graphic card and top VRM clearance, ...)
NH-D15S is the most offset away from the GPU, the only other relatively comparable one is LGMRT, so in the end the choice came for those two as they ticked almost all the same boxes.
Another thing I was looking at is 30mm room between the towers, so I could put in a Phanteks 140mmx30mm thick liquid polymer fan when it comes out (that also took off quite a few coolers from my list). Can't do that on LGMRT in front because of RAM (explained below). Fuma 2 no room in between for 30mm, no room in front for non-slim.
While with LGMRT and Mugen 5 a front 30mm is possible with ram starting in 2nd slot, didn't wanna limit myself to a change that would require to populate all RAM slots (my gut feeling/intuition/hunch was right cause I later found out about dual rank memory setup giving decent performance boost), also wanted to have a cooler that is big enough to accommodate a 140mm Sterrox like fan.
However here comes what
@ciarlatano mentioned, availability and customer support, manufacturer presence, there's none for Thermalright here, while Noctua has the best overall. Additionally, I got burned once 10 years ago by being stubborn about avoiding Noctua for color, price, wanting an underdog (Prolimatech), etc, ..., and I was getting bad vibes about where Thermalright as a company was going to be in the future, which turned out to be right, cause their presence around me has not gotten better, they even closed their main shop in Germany which always had tons of mounting brackets and other stuff, which is not a promising development for their presence outside of China/US, ...
Also the price part is a moot point, logical fallacy, If I'm going to use the cooler for a very long time 10 years, (which I did before), even a twice as expensive cooler is not expensive at all, if I have to replace the cheaper one because at some point down the road I ran into an unforeseen problem with it (Thus I made sure to choose a cooler for which there would be the least possible problems for, AKA the cooler with the best compatibility to performance. And it's 10 years, over that period of time anything ~$100 that doesn't break is worth it.