Jesus does not give the events in order. Verse 15 is the 7th Trumpet. Verse 21 covers the 6 Trumpets. Verse 29 are the Seals. John gives the correct order.
I just showed you how we can be absolutely positive that Jesus is not on earth during the tribulation. Just read what it says and get out of your own way. When you make these wrong conclusions there is NO CHANCE that you will understand.
I'm going to show you that Jesus and John give the exact same order in the end times. There is no need to figure anything out, just read what it says.
1) False Christs.
Jesus-
Matt 24:5 For many shall come in my name, saying, I am Christ; and shall deceive many.
John-
Rev 6:2 And I saw, and behold a white horse: and he that sat on him had a bow; and a crown was given unto him: and he went forth conquering, and to conquer.
2) War
Jesus-
Matt 24:6 And ye shall hear of wars and rumours of wars: see that ye be not troubled: for all these things must come to pass, but the end is not yet.
7 For nation shall rise against nation, and kingdom against kingdom:...............................
John-
Rev 6
3 And when he had opened the second seal, I heard the second beast say, Come and see.
4 And there went out another horse that was red: and power was given to him that sat thereon to take peace from the earth, and that they should kill one another: and there was given unto him a great sword.
3) Famine and Pestilence
Jesus-
Matt 24:7 .................................................................and there shall be famines, and pestilences, and earthquakes, in divers places.
John-
Rev 6:5 And when he had opened the third seal, I heard the third beast say, Come and see. And I beheld, and lo a black horse; and he that sat on him had a pair of balances in his hand.
6 And I heard a voice in the midst of the four beasts say, A measure of wheat for a penny, and three measures of barley for a penny; and see thou hurt not the oil and the wine.
7 And when he had opened the fourth seal, I heard the voice of the fourth beast say, Come and see.
8 And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him. And power was given unto them over the fourth part of the earth, to kill with sword, and with hunger, and with death, and with the beasts of the earth.
4) The Great Tribulation
Jesus-
9 Then shall they deliver you up to be afflicted, and shall kill you: and ye shall be hated of all nations for my name's sake.
10 And then shall many be offended, and shall betray one another, and shall hate one another.
11 And many false prophets shall rise, and shall deceive many.
12 And because iniquity shall abound, the love of many shall wax cold.
13 But he that shall endure unto the end, the same shall be saved.
14 And this gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come.
15 When ye therefore shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand
16 Then let them which be in Judaea flee into the mountains:
17 Let him which is on the housetop not come down to take any thing out of his house:
18 Neither let him which is in the field return back to take his clothes.
19 And woe unto them that are with child, and to them that give suck in those days!
20 But pray ye that your flight be not in the winter, neither on the sabbath day:
21 For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be.
22 And except those days should be shortened, there should no flesh be saved: but for the elect's sake those days shall be shortened.
John-
Rev 6:
9 And when he had opened the fifth seal, I saw under the altar the souls of them that were slain for the word of God, and for the testimony which they held:
10 And they cried with a loud voice, saying, How long, O Lord, holy and true, dost thou not judge and avenge our blood on them that dwell on the earth?
11 And white robes were given unto every one of them; and it was said unto them, that they should rest yet for a little season, until their fellowservants also and their brethren, that should be killed as they were, should be fulfilled.
5) The Signs of His Coming
Jesus-
Matt 24:29
Immediately after the tribulation of those days
shall the sun be darkened, and the moon shall not give her light, and the
stars shall fall from heaven, and the
powers of the heavens shall be shaken:
John-
Rev 6:
12 And I beheld when he had opened the sixth seal, and, lo, there was a great earthquake; and the sun became black as sackcloth of hair, and the moon became as blood;
13 And the stars of heaven fell unto the earth, even as a fig tree casteth her untimely figs, when she is shaken of a mighty wind.
14 And the heaven departed as a scroll when it is rolled together; and every mountain and island were moved out of their places.
6) Jesus Returns
Jesus-
Matt 24:30 And then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming in the clouds of heaven with power and great glory.
John-
Rev 6:15 And the kings of the earth, and the great men, and the rich men, and the chief captains, and the mighty men, and every bondman, and every free man, hid themselves in the dens and in the rocks of the mountains;
16 And said to the mountains and rocks, Fall on us, and hide us from the face of him that sitteth on the throne, and from the wrath of the Lamb:
17 For the great day of his wrath is come; and who shall be able to stand?
As you can see, everything is in perfect order. We don't need to make any incorrect assumptions about whether or not Jesus in on the earth during the tribulation. Jesus and John tell you the exact same story about end times. All we need do is read what it says. 
