We have a file in AfterEffects 15.0.0, using Windows 10.
My coworker started the 2d animation file, and then collected a file copy for me to help out on half of it.
For some reason, my coworker's file cannot be viewed at high resolution, and also can't render at high resolution. I made an .mp4 of my half and brought it in as a layer in my coworker's file. I rendered the entire thing. Coworker's half renders in low res, and my half renders fine. So that implies to me that the problem is with my coworker's .ae file rather than any rendering process.
I saw previous posts here that referred to a similar issue with final renders following the resolution settings of the preview window. Those posts also referred to the bug being resolved in a late 14. version of AE. I've made sure that all the comp previews are set to Full resolution (the fix for that bug), but this did not resolve the issue.