Are you talking about L2 or L3 MTU? Since you refer to a port and the value of 1522 I suspect it means L2 MTU. It is never wrong to have a large L2 MTU since that only states the maximum Ethernet frame size you allow into that port. If you set the L3 MTU on an IP interface (logical or interface in L3 mode, not sure if the VSP supports that) to something other than 1500, then you may start to see problems if you don't know what you're doing.
If your network is a standard setup where routers have an IP/L3 MTU of 1500 bytes (IP packet size), then you can have 1518 bytes L2 MTU on your ports if they are untagged and 1522 on tagged ports. If you have Q-in-Q or more tags, you need to increase the port L2 MTU even further.
An IP packet of size 1500 bytes encapsulated in an Ethernet frame gives you a frame size of 1518 bytes without tagging and 1522 with single tagging.
/Fredrik
