This is clearly Paul, speaking of himself: see 2 Corinthians 12:6, 7, 9, 11; also 2 Peter 3:16.
FOURTEEN YEARS AGO
Some suggest this happened while Paul was in Arabia (Gal 2:1).
But, better, the likely date of 2 Corinthians places the vision around the same time as Paul’s vision of Christ in Acts 18:9
‘Crispus, the synagogue ruler, and his entire household believed in the Lord; and many of the Corinthians who heard him believed and were baptized. One night the Lord spoke to Paul in a vision: “Do not be afraid; keep on speaking, do not be silent. For I am with you, and no one is going to attack and harm you, because I have many people in this city.” So Paul stayed for a year and a half, teaching them the word of God.’ (Acts 18:8-10)
Paul’s visions of Christ are not so common that this is likely to be a coincidence. The mention of ‘fourteen years ago’ might not mean anything to new members of Corinth, but to those whom Paul had baptized during his 18 months setting up the ecclesia it would be a powerful reminder that they owed their conversion to a real direct ‘vision and revelation of the Lord’ (2Co 12:1) on their behalf, without which Paul would probably have quickly moved on from Corinth.
“Did Paul at the same time as this ‘vision and revelation’ in Acts 18:9 have the same view into the Kingdom that Christ gave Peter, James and John at the transfiguration (Mat 16:28)?”
We don’t know.