I reckon the best way from here is to check the internet speed at the office in China, and the file sizes of things that will get uploaded.
If they are big files and slow internet then you should host it onsite the nextcloud, but I dont know if China will allow other companies from accessing the site, maybe it will work if the companies are within china ? not sure though...
If small files sizes then yh host it in the cloud.
You can federate NextCloud systems as well.