Change the oil at a minimum, and do it regularly. Use a quality synthetic high mileage oil and change it again in a couple thousand miles, then change on regular 5k mile intervals.
I have a 17 grand touring and I use idemitsu 0w/20 and purolator b9ss filters.
4.5 L is the Ideal for Mazda 6 2.5 non turbo, I'm from the same country as you. I'm using fuchs titan 5w30 for two years and I recommend you do the same, I noticed quieter engine.
No issues at 150k on my 6. I do not worry but do run pea type injector cleaner every 3-5k and use quality oil that helps prevent off gas issues like Mobil 1 and Valvoline
What brand oil are you using? I noticed a decrease in consumption with Mobil 1 and stuck with it.
they only say you can do that with their Mazda-branded oil. That stuff tends to be expensive.
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