"The disciple John, upon entering the judgment hall, did not try to conceal the fact that he was a follower of Jesus. He did not mingle with the rough company who were reviling his Master. He was not questioned, for he did not assume a false character, and thus lay himself liable to suspicion. He sought a retired corner secure from the notice of the mob, but as near Jesus as it was possible for him to be. Here he could see and hear all that took place at the trial of his Lord. DA 711.1"
"And Simon Peter followed Jesus, and so did another disciple: that disciple was known unto the high priest, and went in with Jesus into the palace of the high priest."
Both passages describe John's presence at Jesus' trial. While EGW adds details not explicitly in John 18:15, the core idea of John being present and observing is shared. EGW's description amplifies the biblical account.