When using ModemManager in OpenWRT, you don’t even need to switch the device to MBIM mode (although you can do it if you want to). The same settings would work for the MC7455 in MBIM mode or in QMI mode. Actually, the same exact settings would also work for other devices as well, see: https://sigquit.wordpress.com/2017/01/07/modemmanager-in-openwrt-take-2/
Note, though, that if using the MC7455 you will want to have at least kernel 4.5, which is when the raw-ip support in the qmi_wwan driver was included.