1) Your desktop's renders may be accelerated by the disk cache, if that's the system you've been working on. For a better performance comparison, "Edit > Purge > All memory & disk cache" before render.
2) To really exploit the server's advantages (cores + RAM), you need to enable multiprocessing in Ae, which means rendering with with Ae CC 2014 (v13.2) or lower. Ae is in the middle of a large architectural transition right now, and Ae CC 2015 doesn't yet exploit systems like this as well as it could.
3) Ae renders almost exclusively on the CPU. The GPU doesn't really matter to rendering performance, unless you are using the ray-tracing renderer, or unless you are specifically using a third-party, GPU-accelerated plugin.