What's the quickest, most efficient way of sending files/proxies to a remote editor (using Premiere) over a moderately slow internet connection?
Sending proxies is also a well established workflow if you choose to go that route. “Offline” and then “Online” editing. 

See the following link for explanation on how to correctly create the proxy files with Premiere Pro

https://helpx.adobe.com/premiere-pro/kb/ingest-proxy-workflow-premiere-pro-cc-2015.html#CreateProxies

Send your Premiere Project and proxy files to your remote editor and receive back the completed project. Import their sequence into your original project and as long as they did not alter the proxies in any way before editing you should be able to reconnect the original media easily.