Hi Edd, firstly thanks for all your work. I deleted the 2015 packages and I tested your diff on my system amd64 OpenBSD 6.1-current (GENERIC.MP) #14: Sat Apr 22 19:55:57 MDT 2017. I had no problems but a 'stalled' download for 'ftp://tug.org/historic/systems/texlive/2016/texlive-20160523b-texmf.tar.xz'. I think it was a problem related to my internet configuration. I used the downloader aria2c(1) and I downloaded the file into the distfile directory. Doing that I was able to build and install all sub-packages. I compiled a few personal TEX documents and it worked but tell me if I should test something else.
tomma