I think I have noticed that if I don't delete already synced content (I have been adding many layers from files) the time to sync increases. I have been adding KML files to my artboard and at first the sync took the average amount of time. I have not been deleting items after they have been synced so as the list of synced layer increases I think I have noticed an increase in time to sync. At first, a file synced in 1:30.00 but now a file takes 15 minutes. There has been a steady increase in time IMHO.
Does this habit cause a slowing down of the sync process? Should I delete a sync layer after it is synced. I have not been doing this because sometimes I need to tweak the KML outside of ArcGis Maps and then resync it. I then just pict the content from the list. This alleviates the steps needed to add it back into the content sync list because I don't have to look for the file on my computer. Thank you in advance.