Realms Server Lag

I apologise if this is not a bug or just servers in Realms being a bit slow but currently my brother owns a Realms server, his computer is a custom built gaming machine which some how causes server jitters and lag, I play his server (just 2 occupy the server) and I am fine, no lag, block glitching or anything. Is there a way to rectify this issue. Lag started at 10pm Australian time. Tried allocating more ram but that didn't do anything.