Well, if your Camry has one of the sludge prone engines, then he’s doubly wrong. If you’re a DIY’r …the cost of some synthetics (many of which are NOT marketed as extended drain oils - in fact, VERY FEW ARE) is not too far above conventional and is easily justified in a (perhaps) situation like yours.
Otherwise, a synthetic will not extend the life of your engine. It will probably last longer itself under more stressful conditions than a conventional. It will take more heat, it will flow slightly easier when cold. It will endure oxidation better/longer.