The 1 Corinthians 15:3-5 material dates to within three years of Paul's conversion.1 This is relevant because Paul converted to Christianity in AD 32-33. (AD 32 + 3 years = AD 35)2
• Galatians 1:18-19 — Then three years later I went up to Jerusalem to become acquainted with Cephas, and stayed with him fifteen days. But I did not see any other of the apostles except James, the Lord’s brother.Notice how in the creed he pays special mind to name these witnesses:
• 1 Corinthians 15:5,7 — and that He appeared to Cephas, then to the twelve. … then He appeared to James,Gary Habermas says this is the “most popular view” [“Experiences of the Risen Jesus: The Foundational Historical Issue in the Early Proclamation of the Resurrection” in Dialog: A Journal of Theology, Vol. 45; No. 3 (Fall, 2006), 288-297.].
• Michael Goulder: “goes back at least to what Paul was taught when he was converted, a couple of years after the crucifixion.” [“The Baseless Fabric of a Vision,” Resurrection Reconsidered, ed. D'Costa (Oxford: Oneworld, 1996), 48.]
The 1 Corinthians 15 creed had been circulating since the almost very beginning of the Christian movement.