As some readers may be aware, I am not a proponent of the view that Galatians 2 and Acts 15 refer to the same event. I believe that Acts 11 is a better fit for Galatians 2. So I especially appreciated the following remarks from Michael Thompson.
“Those who claim that Gal 2 must be the Acts 15 visit typically observe that we have the same people in the same place for a similar issue, and in Acts 11 Luke does not mention a meeting between Paul and the apostles. But is it really credible that if that famine relief trip actually took place, the Jerusalem apostles would have been uninterested in interviewing a man who was preaching a message that did not require Gentiles to be circumcised? Barnabas, the leader of the expedition was deeply committed to the life of the church in Jerusalem, having already given much (Acts 4.36f); presumably there was some affection for him there. It would be very odd if he and the apostles did not want to see each other. Judging from what is said of Barnabas elsewhere, he would have wanted Paul to be included in any welcome (cf. Acts 9.27). The Paul who now proclaimed the same faith he once persecuted (Gal 1.23) would not simply have dropped off some money and walked away without contact with those who shared his basic allegiance to Christ.
“No, if a famine relief visit happened, the travellers would have been refreshed and thanked, and people will talk. The private conversation described in Gal 2 would not have settled the matter of the Jerusalem church’s attitude towards circumcision for the Gentiles; it would take a much larger meeting for that. When Galatians was written, the crucial council of Acts 15 was only about to take place.”
Michael B. Thompson, “Paul in the Book of Acts: Differences and Distances,” The Expository Times 122 (2011): 430–31.