From LedHed's Wiki
DFS is great until it isn't! If you DFS is slow or timing out check if any of these solutions fixes your problem.
DfsDnsConfig
Registry Path: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dfs Name: DfsDnsConfig Value: 1
This causes DFS Referrals to use FQDN. This needs to be set on all DFS servers, not just your file shares. If your DFS-Namespace is stored on a domain controller, then DfsDnsConfig=1 needs to be set there as well.
2012 R2
See: KB3046481
Reference
http://serverfault.com/questions/50789/long-pause-when-accessing-dfs-namespace