Uh, citation needed.
Isn't the 1.5 trillion number the total cost projected out to 2070 or so? (with maintenance included)
You can't take the cost of the whole program to 2070 and then state that nobody would miss the program. Not saying that defense budgets aren't up for debate, but your line of reasoning is not convincing.
Would spending $1.5 trillion from now until 2070 (the time horizon for the F-35 expenditures) avert climate change? Or will climate change happen anyway, and the only consequence will have been a reduction in our abilities to fight other countries for dwindling fresh water resources?
It would be a concentrated effort of just 5 years going all the way at the scale of the Manhattan or Apollo projects, just a question of somebody really wanting to do it. It's just that it's way less sexy.