In general, the larger wheels will not improve the car's efficiency or reduce the fuel consumption.
For any engine, you can draw a graph of the engine's efficiency versus its rpm. Running at very low rpm or very high rpm is inefficient; peak efficiency is obtained at some intermediate value, for example, 3,000 rpm. The car's gearbox will be designed so that you can keep the engine at approximately the optimum revs whatever your speed.
The only circumstance under which larger wheels might help would be if you're driving at a speed higher than the maximum speed for which the car was designed -- for example, if you're doing 200 kph in top gear and the engine is at 4,000 rpm. At this top end of the range, the larger wheels would allow you to maintain the same speed while the engine is at a lower rpm, thus allowing the engine to operate closer to its optimum revs. But for lower speeds, the gearbox will allow you to keep close to optimum revs, and the larger wheels will offer no advantage. (In addition, the larger wheels will make it harder to maintain optimum revs at very slow speeds, for example, starting up and climbing steep hills.)
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