trying to understand your notation, treating HO track (0.65" gauge) as if it were 15" gauge would yield a scale of ~1:23. is that what you are shooting for?
you might try a lower case 'N' to be a little more consistent with other narrow notation as in HOn3, On30 or in your case, ...Gn15. at first i thought this post was of Great Northern interest.
as much as i hate using the 'G' notation in reference to any scale, i'll have to admit it's probably most forgivable when referring to original LGB which has been estimated to be in the ~1:23-24 scale range.
cheers for taking on a nontraditional modeling challenge.
...gary