Data usage of LoL

How much does connecting to LoL (logging in), starting ARAM game and then playing 1 ARAM game take data? I have a limited amount of data on my internet and we have used more data than normally :/ My parents think that LoL is eating all of our data. If I could get an answer from a RIOT employee then it would be perfect ^.^ Also does anybody know where I could find the amount of data I have used? I am using MacBook Pro with the newest OS.
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