Hear I would like to share my exp. as well, My punto have clocked 22k in 7 months, and i also found the same Tyre trade issue, then the SA at the FIat authorized service center explained me that, due to more steering of front wheels compared to rear, the trade of tyre gets worn out on the outer edge, hence it is recommended to have a tyre rotation done at proper interval, (what is the time to change the tyre our experts will guide us, but for me i guess after 60,000 KM we should change the tyres.) About Oil, in Diesel engine if we change the oil and run the vehicle for say 400-500 km and then if you check the visibility of engine Oil it will look like as black as it looks after the 15k km. so its Ok, if you are using Fully Synthetic oil. then no problem in changing at an interval of 15k Km and if you are using semi-synthetic oil then it will be better to change after 5-7k KM.