Nope, not all Israel.
Jesus gives the answer in verse 16:
16 then those who are in Judea must flee to the mountains.
Judea is the name of the mountainous southern part of the Land of Israel, so Jesus was saying to flee to the mountains OF Judea (i.e. the unpopulated areas in the hills of Judea). Being that the Temple in the city of Jerusalem was Ground Zero, the target, as it were, it's the last place you'd want to be, and fleeing on foot without returning to pick up provisions at one's home is the point he was making.
Wikipedia mentions the seeming fulfillment of this prophecy, in 70 CE (some 40 yrs after his death):
In 6 CE, Judea came under direct Roman rule as the province of Iudaea. Eventually, the Jews rose against Roman rule in 66 CE in a revolt that was unsuccessful. Jerusalem (and the rebuilt Temple) was destroyed in 70 CE and much of the population was killed or enslaved.
Maybe might've been good to take Jesus' advice back then in 70CE, even if it's not the way JWs want to turn it into a modern-day prophecy.
also from Wikipedia:
Bar Kokhba revolt
The Jews rebelled again 70 years later under the leadership of Simon bar Kokhba and established the last Kingdom of Israel, which lasted three years, before the Romans managed to conquer the province for good, at a high cost in terms of manpower and expense.
After the defeat of Bar Kokhba (132–135 CE) the Roman EmperorHadrian was determined to wipe out the identity of Israel-Judah-Judea, and renamed it Philistina (Syria Palaestina, after the ancient enemy of the Israelites; the Philistines). Until that time the area had been called "province of Judea" (Roman Judea) by the Romans. [ 11 ] At the same time, he changed the name of the city of Jerusalem to Aelia Capitolina. The Romans killed many Jews and sold many more into slavery; many Jews departed into the Jewish diaspora, but there was never a complete Jewish abandonment of the area, and Jews have been an important (and sometimes persecuted) minority in Judea since that time. [ 12 ]
So even if you don't like the idea of applying Jesus' prophecy to 70CE, you get a chance to declare it fulfilled in 135CE (or a prophetic double-play, if you prefer). And if the JW version of the Great Tribulation comes true, then Jesus gets credit for a prophecizing three-peat. :)