We have established a new OTA server for oversee users, this should be an obvious improvement over the previous China server as there is a limited data rate to connections outside China. If you are upgrding from v3.1en, you should connect to the new OTA server automatically, If your N5ii is still using v2.1en, I'll suggest you perform a manual upgrade this round otherwise you'll link to the OTA server in China and that will be significantly slower.
I went from 3.1 to 3.3 via OTA in the US and it worked great. No issues! Thanks!