Proxy Ram?

Hello guys,
I know that this question was asked frequently, but how much RAM is suitable for my BungeeCord proxy? I have 6 servers each with 4GB RAM, and I get about 90 players in each server. But what about the proxy? How much ram is it suitable?

Thanks

P.S: Sorry if that question is too easy for you , but can you explain to me what is a proxy?