But the Abomination of Desolation (AoD) disciples are warned to flee after they see the AoD set up. If this referred to the desecration of the temple by the Roman standard entering its precincts, that happened well after the siege had been put in place, and it would be too late for the disciples to flee.
Verses 16-20 comprise the instructions that the Jew-Christians were to follow according to the recognition of what is being illustrated in verse 15.
'When ye therefore shall see...'
[then]
'follow these instructions'
(And don't waste any time doing it.)
There was a three-year seige before the Romans took the city and destroyed the temple.
The Jew-Christians followed the instructions before/as the seige began.
What did they 'see' - before/as the seige began - three years before the temple was ever touched or destroyed - that they instantly recognized as being what was illustrated in verse 15?
hint:
( whoso readeth, let him understand: )
~
What they saw was exactly what is described in the Luke account.
And, it was precisely that that they were warned to flee when they saw it.
There was no AoD circa 70 A.D. - before, during, or after the siege.