Ah ok that particular modem runs by default in Hilink mode, which means it’s basically doing all the routing/etc on the modem itself (think of it more as a “modem/router”). So when you connect it, it should just be showing up as an extra network interface. Dont worry about the QMI/MBIM stuff not applicable here as the network interface should be more than capable of handling the bandwidth.
My suspicion then goes back to the original point of CPU power on the AR150. You can reduce the CPU needed by turning off NAT, but that pretty much defeats the point of using the router unless your only intention is to be able to share the connection with more than one device at a time?