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I'd never recommend running an engine for 15000kms on the same oil. Some engines are easier on oils than others (operating temps, shearing etc) and Audi/VW engines do not have a good reputation, rather they sludge up very easily and are very hard on oils. Long life or not, 5000-7500kms would be as far as I'd go. Have a look over on the BITOG forums and check out some UOA's and see the wear metals increase when pushed past 5-7.5K kms, not worth the extra wear and tear IMO, I'd rather just change the oil.
Fuel additives I have on good authority (fuel injection specialist who was a good mate of my tuner and whom I spent a fair bit of time with) are a bit of a wank. Some will work a little, but good quality 98RON has additives that should keep things pretty clean, and that after about 40-50K kms, you should pull the injectors and have the ultrasonically cleaned (~$22 per injector). No additive comes close to a proper ultrasonic clean. Just use 98, and get them properly cleaned every 50K kms or so, much cheaper than buying fuel additive all the time.
Fuel additives I have on good authority (fuel injection specialist who was a good mate of my tuner and whom I spent a fair bit of time with) are a bit of a wank. Some will work a little, but good quality 98RON has additives that should keep things pretty clean, and that after about 40-50K kms, you should pull the injectors and have the ultrasonically cleaned (~$22 per injector). No additive comes close to a proper ultrasonic clean. Just use 98, and get them properly cleaned every 50K kms or so, much cheaper than buying fuel additive all the time.
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