We recently installed a new server with Windows Server 2012 O/S
Access the shared-folders on the previous Windows 2003 Server were much faster than on the Windows Server 2012 O/S.
It seems that the server goes into "sleeping mode" and then when re-accessing the shared folder, it takes about 3 - 5 minutes to "wake-up" and make the contents available.
Once logged in and actively working on the server, it is fast. When left for an hour or so, it takes another 3-5 minutes to initiate the network connection to the server / shared-folders.
I've seen related articles with users complaining about a similar problem since Windows Server 2008. I am unable to find any solution as yet ...