There are reports of performance issues and repeated reconnects when using Outlook 2013 and MAPI over HTTP in Exchange 2013. The problem is that the header that the server uses to specify the connection keep-alive period as the server is processing the request is ignored by the client.
This is fixed in the November 2015 update for Outlook 2013, KB3101488: https://support.microsoft.com/en-us/kb/3101488.
For more information about MAPI over HTTP and how to configure it, see here.