Isn't the Nintendo Network just a profile though? Don't see what they'd have to do with the game other than that.
Maybe you'll have good luck with LAN - it's tons slower for me. I still wonder if the USB port on the Wii U is old (like 2.0 vs 3.1) and that's why the data transfer is so slow. LAN is a great back up though - I go LAN if the weather is being stupid or if I have others on my WiFi...which isn't the case usually because I lockdown my WiFi, LOL - I disconnect everything and power cycle my router/modem every time before I turn on the U.