First off, nice on the Mikrotik! (I'm a Routerboard/Mikrotik fan myself!)
Ok... so I think what you are seeing is the normal chatter that happens between the XMPP clients and the XMPP server... things like presence packets, ping packets, etc all go back and forth quite often.
I don't know of OF 3.6.4 supports the Load Statistics plugin (OpenFire Admin Page --> Plugins --> Available Plugins --> Load Statistics), but if you install that plugin it will show you the packets being sent around on your XMPP network, how many users are active, and the general "load" on your server.
Is this what you were looking for?