Two thoughts:
(Thought 1) Since passenger traffic is something you mention a number of times, I'd go with at least an 18" visible radius, with larger if you can fit 'em in. Keep the 15" radii where they're mostly concealed. Of course passenger equipment will work most of the time on a 15" radius, but it'll work for sure on 18" minimums, and look a helluva lot better. You might have to give up a bit of isle width, and as important as that is, it's not "all important" and a little sucking in the gut is worth a better looking train.
(Thought 2) You've got some areas with long straights which run parallel to your fascia....b o r i n g. Although it's strictly cosmetic, putting some extra-large cosmetic curves in those areas or running your fascia at an angle to your mainlines will make the layout more pleasing to the eye. "Flowing" fascia is also something that improves the layout's ambiance and is easy to do when you're planning your benchwork. Although it's inevitable that your mainlines will follow the fascia sometimes, it's a good idea to not allow that to happen very much.