SSH by definition is secure as all traffic is encrypted whilst in transit across all networks. Wiretapping is not something that you have to worry about with SSH.
The entire purpose of SSH is to create an encrypted connection between the client and the server to ensure that none of the information transmitted between them can be seen on any network other than in its encrypted form.
Changing the port would do little to disguise the traffic anyway but it is not necessary, as like I said SSH is completely encrypted. This would only be 'Security through Obscurity' at best anyway which is not security in anyway, shape or form.
If the system administrators have your SSH keys then wiretapping would not be your concern as they could directly connect to the server let alone decrypt traffic sent over the network.
It is unlikely they have your keys as these cannot be sniffed out when sent, as they are encrypted in transit.
View Network Connections
Network admins will be able to pinpoint that your user account and computer is connected to a specific IP address on port 22 but that's all they will be able to see. I would not consider this a great concern as long as your servers security is correctly configured.
On an Internet facing SSH server, one or two network admins are most likely your least likely people to be targeting your server, you will most likely find that people are already constantly attacking it, this is called 'the background noise of the Internet'. This can be seen by reviewing your auth logs. As long as only key auth is enabled this is not a concern but I personally like to run fail2ban too to filter out these connections.
SSH Security Concerns
The biggest concern when using SSH is to ensure that attackers cannot gain access to the SSH server itself, normally through brute force attacks but this can also be done via much more sophisticated targeted attacks.
The simplest and quickest way to secure an SSH server is to enable key auth authentication rather than password authentication.
If possible you should remove your SSH server from the Internet and only allow access either internally or through a VPN connection.
There are many more ways to secure an SSH server such as two factor security and packet knocking.
It is for these exact reasons that telnet is largely not in mass use anymore. As it does not encrypt the connection, everything is sent across the network in plain text, including the password, meaning that anyone on the network that is packet sniffing or monitoring connection logs can easily obtain username and password information and anything else sent over a telnet connection.
More information about SSH can be found here...
Man page for SSH
OpenSSH Website (One of the largest SSH Servers)