If the universe was formed supernaturally over fifteen billion years and God in His wisdom chose to refer to the time as six days, then that is what He did.
1)The entire purpose of fifteen billion years is to give the universe time to form naturally, without any Divine "interference." Notice no one ever allegorizes the six days to six centuries or six seconds? It's always the exact amount of time it would take for the universe to form "naturally."
2)I guess J*sus didn't really turn the bread and wine into his flesh and blood but just put it that way.