Good point. Personally, I think by the time Acts 10 arrived, Peter was sensing in his heart that the Jewish nation was not going to ever accept Jesus as their Messiah, with the first martyr Stephen.
And during the time of Acts 10 and 11, when he saw that God began to grant Gentiles salvation without them having to be circumcised nor water baptized like the Jews, he realized the time was indeed up for Israel.
Hence he was able to defend Paul's ministry to the Gentiles by the time Acts 15 came along.
Thought you might be interested in the revelation I recently received from God. I posted this to Hevosmies but didn't know whether you would see it:
I have never doubted that all instructions given at Pentecost (repent, get water baptized in Jesus' name and receive the Holy Ghost) were required and that a specific sequence was not necessary. However, every record in the bible is as it is for a reason.
I wondered and prayed about the significance of the Gentiles receiving the Holy Ghost first and afterward being water baptized in Jesus' name. Praise God that after accepting things by faith there are times He gives us a glimpse into why an event unfolded as it did:
It is common knowledge that God will always confirm His concepts in the Word by at least 2 examples/witnesses. (1 Cor 13:1, Matt 18:16) One can see God's principle at work in the sequence of events that took place when the Gentile population was presented with, and obeyed the gospel message in Acts 10.
Initially, the Jewish population were the only ones given access to the spiritual re-birth via the gospel message. (Acts 2:38) The Gentiles were unacceptable to God; they were considered unclean. Jews did not associate with Gentiles let alone share the gospel message with them.
God was soon to make some changes and there would be no second guessing exactly what God wanted. God gave Peter a vision. (Acts 10:9-17) In the vision Peter was shown foods that had been unclean but were now considered clean. Peter wondered what the vision meant. (Acts 10:17-20) On the same day, men were sent to Peter by a Gentile named Cornelius.
Peter asked why Cornelius sent for him. (Acts 10:29) Cornelius said he wanted to hear all the God had commanded of Peter. (Acts 10:33) While Peter was sharing the message of Jesus' death, burial and resurrection the listeners were filled with the Holy Ghost and spoke in tongues. (Acts 10:44) Peter and the Jews with him were astonished that God had chosen to fill the Gentiles with His Spirit.
God had made it clear by two examples that the Gentiles were acceptable to Him and could have their sins remitted in the waters of baptism as well as the Jews. That is why Peter said, Can any forbid water that these should not be baptized that have received the Holy Ghost as well as we?
Later Peter would tell the Jewish leaders that he had no right to withstand God after seeing God had filled the Gentiles with His Spirit. It is clear what Peter meant. It was not up to him to withhold water baptism from the Gentiles. God made His wishes clear by filling them with His Spirit.
Acts 11:17-18
Forasmuch then as God gave them the like gift as he did unto us, who believed on the Lord Jesus Christ; what was I, that I could withstand God?
When they heard these things, they held their peace, and glorified God, saying, Then hath God also to the Gentiles granted repentance unto life. REMEMBER WATER BAPTISM is the baptism of repentance for the remission of sin. (Luke 3:3)