The overthrow of the great city Babylon was seen in chapter 14:8-10, but in chapters 15 and 16, the seven last plagues result in the judgment and wrath of God on the false Roman church system, the great whore. The chapter 14 gave us a summary largely of future events. Chapters 15 through 19 present those same events, but in more detail. These chapters (15-19) are all connected with the fall of spiritual Babylon.
The opening of the seventh seal (chapter 8) resulted in the triumph of Christianity over Roman Paganism. This was followed by seven trumpets (chapters 8 to 11) which led to the overthrow of the western Roman Empire by the Goths, Vandals and Huns, and the ruin of the Eastern Empire by the Saracens and Turks. The seventh trumpet, the last trumpet, takes us to the close of secular history with the trump of the Archangel.
The seven vials (chapters 15,16) also give the history of an epoch, and, like each of the series of seven, bring us to the end of that epoch. They present the series of calamities that first weaken and then destroy the power of Papal Rome.
Chapter 15 opens with “And I saw another great sign in heaven, great and marvelous, seven angels having the seven last plagues” (v.1). That is 7 angels with 7 plagues which are to be poured on the earth by use of 7 vials, but they don’t come out until verse 6.