If the plagues last a year, do you think the world will understand what is happening that whole time?

Personally, once the plagues start to fall, I believe there is a year or less left in earth's history as we know it.

Revelation 18:8; Therefore shall her plagues come in one day, death, and mourning, and famine; and she shall be utterly burned with fire: for strong is the Lord God who judgeth her. (KJV)

This isn't the only verse, but, this is what I believe. Babylon has fallen and God's people are delivered from Satan's power as the angel with the chain is binding him to the earth. (Rev. 20:1-3)

Revelation 18:10; Standing afar off for the fear of her torment, saying, Alas, alas, that great city Babylon, that mighty city! for in one hour is thy judgment come. (KJV)

This one hour is from the perspective of those who benefitted from Babylon. I believe this "one hour" could be 15 literal days. Referring to Daniel 11:45, Satan claims this earth as his own! Babylon is set up the way he wants it and he denies Christ the right to return.

Why?!? Because in Proverbs 10:30, the Bible teaches that never will this earth be inhabited by 100% wicked human beings. Never. With Job God makes the point that He only needs one faithful follower to claim this earth as His.

Satan now claims that he has eliminated all of God's people and obliterated the knowledge of the One, True God from off the earth. (Ellen White term) That is why in SpM 2.1, when the Fit Man grabs hold of the scapegoat, if Christ loses His grasp Satan will destroy all of Israel. But, God is true to His promises and delivers His people at this time.

The ten horns or kings of Revelation 17 burn the whore and the plagues start falling. I believe this can all happen in 15 literal days.

But, God also says He will have 144,000 sealed to His kingdom. They will be delivered from Satan at this time and preserved until the Second Coming of Christ.

The synagogue of Satan will worship at the saints feet. So, some people will realize what is happening. But, most will not. Just like in the days of Noah, most will be marrying and given in marriage and so on....

Doesn't Ellen White write about the plagues happening first and then the people turning on their pastors and each other?

Yes. I don't remember though if it is before or after the plagues start to fall. Do you think this will make up most of the people? Remember, we are talking world-wide at this point in history.