Locking the cabin door virtually eliminated the threat of turning jetliners into terrorist weapons at a tiny cost. But on top of that we've cost the country maybe a trillion dollars in excessive and invasive security procedures to prevent planes from being blown up. The TSA is only one part of those costs, longer travel times, reduced travel and lost liberties are a big part of it.

The value to terrorists blowing up an airliner is relatively small, there are far easier and cheaper ways to kill a few hundred people to make a political statement.

So my real question is, if we reduced spending on airport security, and reduced the level of security significantly so that we shaved 15 mins on average off every trip, would it be worth accepting a plane being blown up every few years?

Every year the US has nearly 1 billion trips by air. If you value travelers time at $20/hour, saving 15 minutes per trip directly saves nearly $5B a year. If the cost of saving those 15 minutes per trip is 50 lives per year, we are valuing each of those lives at $100m each. That seems incrediably excessive to me. Of course this is just a rough estimate, run your own numbers but it's hard to imagine the costs get down to a barely reasonable $10M per life level.

and remember that doesn't include the cost of the TSA or the cost of flights not taken.

How are you assessing the value of a human life?

How are you assessing the value of a human life? I don't know of any study has ever gone above $10M.