You can do whatever you want, but these cars are inexpensive enough to maintain it seems reasonable to follow the manufacturer's recommendations. If I were to extend them I might (a) change oil and filter at 15K, or (b) change the filter every 10K and oil every 20K. When you try either of these you could first get a baseline oil analysis at 10K, and then another at 15K and 20K. I think I did this once years ago on my car and running the oil 20K miles didn't seem harmful. However, the analysis doesn't cost much less than the change, so why not change the oil and filter?