Yes, that's true, or at least true theoretically. And the issue is related to the quad/starquad nature of the cabling, not specific to copper per se.
Quad cabling will have higher capacitance per foot, and that can degrade high-frequency response. Whether it is much of a concern with 15' mic cables as opposed to 200' runs of cabling I don't know.
Still, it is something to consider when choosing cabling. I don't know that quad cabling is the best choice in this regard. Cabling that is part of a snake or permanent install might go very near fluorescent lights, dimmers, electric motors, etc, etc that can create a noisy environment, so quad cabling could well make sense. In a taperssection, I'd guess we're much farther away from those sources of noise, though probably much closer to cell phone noise.
I don't know the right choice. When I was making cables, I started with quad silver since I thought iwth the noise aspect for mic cables it would make sense. Then I found that far more of my orders were for custom short ICs that would be down in a gear bag, so I decided to change to regular two-conductor cabling (non-quad). Of course, at the time, I didn't personally own or use a cell phone, so I hadn't given that aspect much thought then.