I have been experiencing the same terrible sync performance both from my iPad and my Mac Pro (wired ethernet).
I have a new iPad Pro with Lightroom installed. I have 70 photos that I transferred from my camera’s (Fuji XT-2) SD card to Lightroom. The RAW files are approximately 50MB each. A speed test run from my iPad shows a minimum of 3Mbps upstream speeds (120Mbps downstream). In the last 3 hours, Lightroom has managed to sync 4 images.
Unfortunately, I’ve seen similar performance from my Mac Pro on a wired Ethernet connection and don’t see any solutions to improve the sync speeds.