It may well be that the type of treading the grapes is ALWAYS a reference to judgment.
Isa 63:1-6
Who is this that is come from Edom, with red garments from Bosor? thus fair in his apparel, with mighty strength? I speak of righteousness and saving judgment.
Wherefore are thy garments red, and thy raiment as if fresh from a trodden winepress?
I am full of trodden grape, and of the nations there is not a man with me; and I trampled them in my fury, and dashed them to pieces as earth, and brought down their blood to the earth.
For the day of recompence has come upon them, and the year of redemption is at hand.
And I looked, and there was no helper; and I observed, and none upheld: therefore my arm delivered them, and mine anger drew nigh.
And I trampled them in mine anger, and brought down their blood to the earth.
Yeah, I agree about the harvest of the grapes, as it is made obvious that this second harvest is referring to living people being thrown into the winepress of the wrath of God Almighty. But it is the first harvest that is not clear. We have the harvest/gathering of the church prior to God's wrath, which I believe is represented in Rev.4:1. Then we have the gathering of the Male Child in Rev.12:5 where they are caught up to God and His throne. Then we have the great tribulation saints resurrected as stated in Rev.20:4-6, which takes place after the Lord returns to the earth to end the age. So, who are those being harvested at that first harvest in Rev.14:15-16?
Until the Lord reveals the answer to this, I will not make a claim nor teach it, but will keep it in my spiritual cupboard until then.