I don’t know the answer to your question, but back when I had unlimited tethering with fast 4G, I would basically just have it on all the time to use my laptop

I don’t know the answer to your question, but back when I had unlimited tethering with fast 4G, I would basically just have it on all the time to use my laptop on the go and treated it like home WiFi. So even though I would have home WiFi and be connected while at home, I would still rack up 10+GB of usage monthly. That is to say, I can imagine hitting 17GB could be common every month even with home WiFi depending on the culture of usage.