“There is good news and bad news when it comes to the 15,000 mile oil change — a standard five times longer than those often recommended by the quick-lube merchants. The good news: Yes, it is possible with certain vehicles and motor oils, to do so with no harm to your car.”
You an read the rest of the article here----> https://autos.yahoo.com/blogs/motoramic/the-guide-to-whether-a-15-000-mile-oil-change-works-for-you-134321080.html
To boil it down:
Whether you use conventional oil or synthetic oil, “Your engine will probably outlast your interest in the car.”
If the car is still under warranty, follow the oil change requirements in the owner’s manual. Don’t extend your oil change interval, even if you choose to upgrade to synthetic oil.
Unless you have an oil analysis performed, you’re just speculating. The article recommends getting two oil analyses done, one with the oil type and change interval you’ve been using, and another after upgrading to long life synthetic oil and extending your oil change interval.
Once you confirm, via oil analysis, it is safe to use synthetic oil for 15,000 mile intervals, changing the oil more often is wasteful.