Why did u use 15w40? If u follow the honda manual it states at least a minimum 5w30.
Therefore changing to 10w30 will restore the engine performance. It will improve the FC alot also.
idsi engine dont need such heavy oil even at such mileage.
The engine operating temperature isnt that hot either.

Fyi my family owns the IDSI since new and still send back to Honda SC for service. They also use Honda 10w30.