I looked through the two Credo's and 3-15 SWFA for the last 5 minutes of legal hunting light here on my property (official sunset plus 30 minutes).
I could have taken a 200 yard shot with all three (open space, not in timber, not against dark timber). My aged eyes couldn't really tell the difference between the 2.5-15 Credo and 3-15 SWFA on 9x magnification other than the reticles. Didn't need illumination on 9x for any of them. They were both slightly brighter than the 2-10x36 Credo (to be expected).
Trijicon makes no claim of using "HD glass" that I could find, so perhaps I shouldn't be surprised.
Between the FFP reticle on the Credo 2-10 and SWFA, I prefer the SWFA. The Credo has a total of 24 mils between the thick horizontal bars. The SWFA has 12 mils between the bars. At lower magnification, the SWFA reticle is much more prominent and usable than the Credo without illumination. When illuminated, the Credo FFP reticle tree is entirely illuminated.
Honestly, I was surprised. I've been a Negative Nancy on the SWFAs for years now (except the 5-20HD), mainly due to the excessively tall turrets. Mounted on my rifle, they don't appear quite as obnoxious as I expected. (I only just received the SWFA 3-15 yesterday and mounted it on my rifle last night).
Just my $0.02...ymmv.