206 1.4 gasoline engine oil selection

friends I'm going to have the car maintained. 15w40 is used for the engine as far as I know. what would you recommend as a brand? By the way, there is also LPG in the vehicle.

I know 10/40 castrol in gasoline vehicles

10/40 castrol a3 / b4 synthetic technology

15/40 will not be 5/40 when you go to mobile or castrol site, but if you put 10/40 because it is cheap, most people will decrease 5/40 thinner and burn oil over time, but if you say later, add 5/40 healthier engine and relaxation. It makes sound cutting, I made it 5/40 a month ago, I had 10/40 before, I did 1000 km more, I do not reduce any loss, I take 1 liter and add 1 liter. and it is healthy, I said, whatever oil site you look at and look at it, our models will recommend 5/40 oil, including factory oil, total