Contradiction with John 18:36
Jesus explains His kingdom is not of this world, whereas Mark 15:2 involves an implication of earthly kingship.
John 18:36: Jesus answered, My kingdom is not of this world: if my kingdom were of this world, then would my servants fight, that I should not be delivered to the Jews: but now is my kingdom not from hence.
Contradiction with Luke 23:2
Accusation that Jesus claimed He is a king, but in Mark 15:2, Jesus refrains from claiming earthly kingship.
Luke 23:2: And they began to accuse him, saying, We found this [fellow] perverting the nation, and forbidding to give tribute to Caesar, saying that he himself is Christ a King.
Contradiction with John 6:15
Jesus withdraws to avoid being made king, contrasting with the acceptance implied in Mark 15:2.
John 6:15: When Jesus therefore perceived that they would come and take him by force, to make him a king, he departed again into a mountain himself alone.
Contradiction with John 19:15
The crowd rejects Jesus as king, whereas Mark 15:2 involves acknowledgment of His kingship.
John 19:15: But they cried out, Away with [him], away with [him], crucify him. Pilate saith unto them, Shall I crucify your King? The chief priests answered, We have no king but Caesar.