Is it there a way to selectively upload only new items?
There are many elements that affect the length of the upload process, for example, Related posts – when you add a new post the list of related posts changes on all post pages.
Have a look at the “How to speed up rendering process?” article, it may help you optimize your upload time.
Do you appreciate the support you've received today? If so, consider donating to the Publii team by clicking here; we'll be sure to use your donation to make Publii even better!