Running xfs_db(8) to examine the superblock gives three relevant values for the formatting of inode numbers on this file system.
agcount' value of 8 or 23 means that three bits will be needed to specify the AG number.
inopblog' value of 4 means that there are 24 or 16 inodes per filesystem block. This makes sense since 16 256 byte inodes can fit in a 4kB filesystem block.
agblklog' value of 15 indicates that each AG has 215 filesystem blocks in it. This is expected since the mkfs.xfs output reported an agsize value of 32768 blocks.