The link check in this context is used as an occasional ACK just to determine if the network is still available.
It is a compromise between ACKing every packet and sending packets into the air hoping the network is still there.
There is no method to determining if a single packet was received by the gateway in this scenario. Just that in general the gateway is still able to hear the device. In the example the success ratio could be as little as 1/15 packets, but an action can be taken when it reaches 0/15.