Yes this is probably a server thing, rather than a processing thing, there are a few things you can look at.
underneath the hood, uSync will be warning you if it thinks the notification part of the save/publish is taking to long. and you will see warnings like this :
“Processing notifications is slow, you should check for custom code running on notification events that may slow this down”
this means something that is running code on a ContentSaved, ContentPublished, MediaSaved… type event it taking a longer than normal (over 2 seconds per item) amount of time to execute, and you should take a look to see if you have any custom code doing strange things. You can have things happening in notifications that are fine, until they get under load of loads of things being saved and then they slow right down 
You should also check examine settings - but if you are running local, with reasonable disk speed that’s usually not a thing.
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You can increase the “page size” for imports and this will increase the number of items per request that the processing step handles (by default it’s 25 or 50 depending on version, for media its lower at 5).
Changing this probably won’t speed it up a lot - it will remove some of the overhead for the request (so the auth, validation, packing/unpacking will happen less) but all of that is actually a very small bit (sub 1/2 a second max) part of any request. and upping this number puts you closer to the risk of timing out, locally that might not be an issue, for example on azure it’s around 240 seconds and you will hit the wall.
Media and Blob storage
If there is actual media items in the import (and the media files) then i can be quicker to move the media files using something like storage explorer, and only have the media entries (so don’t include the files) in the uSync export.
when you import this, the files will already be on disk, so there is a lot less coping, and uSync/Umbraco just created the db entry for the media - which can be a bit quicker.
For clarity the ‘processing’ steps when you are importing is only really doing the following:
- you upload the import
- it’s extracted to a temp folder
- the exporter loops through the folder (so you see lots of steps). importing items just as if you have done it via the uSync dashboard, execpt it does it in ‘pages’ to skip timeouts.
I would just like it to do some faster.
Unfortunately, I’m trying to update a “staging” database to replicate a potential go live situation. However, I think what this has shown is, I might need to copy the DB down locally, do the uSync Import on a local DB server and then push the DB back up to Azure as a work around which will be faster - I would hope!