Mark 16:15 And he said unto them, Go ye into all the world, and preach the gospel to every creature.
Mark 16:15 is not a genuine verse of the Bible, it is a verse that is addition because in ancient copy of the Bible, Mark 16:15 is not there especially the ones in dated back in 1st, second third century
Are you going to preach to the dogs 🐶 , goats 🐐 , fish 🐠 in the Sea? The work creature there means so much like the one in Roman 1:25
Romans 1:25 Who changed the truth of God into a lie, and worshipped and served the creature more than the Creator, who is blessed for ever. Amen.
The word creature in the above Bible verse does not mean only human being. If you reach from verse 23 to 25, you would what Apostle Paul mean
Romans 1:23-25 And changed the glory of the uncorruptible God into an image made like to corruptible man, and to birds, and fourfooted beasts, and creeping things.
Wherefore God also gave them up to uncleanness through the lusts of their own hearts, to dishonour their own bodies between themselves:
Who changed the truth of God into a lie, and worshipped and served the creature more than the Creator, who is blessed for ever. Amen.
Matthew 28:19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:
The above verse doesn't say all creatures, it says All Nations, especially Men because men made nations and this is where understanding is neccesary, preach to every creature, you would have to preach to animals too
We don't even need to go to one place or the other before we preach, a lifetime is not enough.
Mark 16:15 is not a part of the Bible, it is an additional