Acts 15 does not say that God did not mean it when he gave the feasts to all men. God had the prophets repeat over and over he was speaking to the foreigners among them, also. God did not make one world with one set of ways it was to operate and a separate world for his chosen people. The feasts are not a custom of the Jews that is not to be honored unless you are Jewish.It's not that hard to understand. Just read Acts 15.
All the customs that we do not need to follow were like being guided on a walk to a destination. Cutting foreskin was to mark belonging to God and eating only pure foods was to guide to keeping pure. The feasts do not lead to a spiritual truth, they are to honor Christ, God's salvation of our souls. The Lord tells us they are for all generations.