Facetime poor connection on Wifi

So I've been having a lot of issues with Facetime, maybe others have experienced similar issues:

I usually facetime with my parents who live overseas, they have a 2Mbps/512kbps DSL and I have a 200/5Mbps connection. My mom uses an iPhone 7+ on wifi (2.4ghz) and I use an iPhone 7+ or xs on Wifi (either 2.4ghz or 5ghz)

No matter where I am in the house or close to the router either of us will get poor connection, I first thought it was her connection causing this issue, but as soon as I switched to data on my end (LTE with T-Mobile), all the problems went away.

When the problems happen usually they can't see me but can hear me and I can see and hear them, which points to the fact that maybe my uplink is problematic or that maybe facetime has issues on wifi.

The only thing I noticed this morning is that when I did the Facetime video call with my mother yesterday on data and in the one hour it used 250Mb data over LTE, last week I did a Facetime video with my father for an hour, and it was on wifi and it used 1.52Gb of data over wifi, why does Facetime need considerably more bandwidth over wifi ?