Paul went to Jerusalem for 15 days precisely to receive information on Jesus.
This is relevant because such information would be hard for Paul to miss. As Paul stayed at Peter’s, Peter would have been eager to deliver his account to Paul.1
Gerhardsson is nothing here how, in Paul and Peter's overtly Jewish context, pupils and teachers meet in just this way such that “the word of the Torah was between them”. This is a Jewish context for exchanging doctrinal statements from teachers and predecessors.
• Birger Gerhardsson: “…a man with Peter’s commission does not waste a fornight talking rubbish. It [sic] can be little doubt that during this time the word of Christ ‘was between them’” [Memory and Manuscript (1998), 298.]
But wait, Jesus biography and creedal statements are not “the gospel”.3
• Richard Bauckham: [On Galatians 1] “It was on the strength of this revelation [from Jesus] of the gospel message that he already proclaimed the gospel, with full apostolic authority, in the period before he visited Peter in Jerusalem (vv.15-17). What he lacked, however, was detail about the words and deeds of Jesus, and he may have come to see the need for this during his period of mission in Nabatea (Arabia: v. 17). [Jesus and the Eyewitnesses 2nd ed. (Eerdmans, 2017) 267.]