We will be releasing patch 1.5.15, a server only release, on Feb 16th. There is no planned global downtime for this patch as it will be 'rolled' out to each individual server one at a time. Each individual simulator may experience a brief downtime. Sorry for any inconvenience this will cause.
The primary purpose of this patch is to update the simulators with minor infrastructure changes necessary for the deployment of release 1.6.
Chris