How much will it cost to replace your engine vs. doing more frequent oil changes?

Get conventional oil and change it every 5k miles. You don’t want to risk on your engine. 

You should be changing the oil more frequent than every 13,000-15,000 miles, especially if you want the engine to last as long as possible.  It should be every 5,000 miles or 1 year, whichever comes first.

That’s good quality oil, and I am sure it can retain most of its viscosity that long. But you have to consider more than viscosity, there are dirt and contaminants that can build up in the oil as well as gasoline dilution. Plus, you can lose oil due to leaks or combustion. 

So definitely, I’d go no more than 10k, and preferably 5k. There may be advantages to an oil like Mobil 1 “high mileage formula” that contains additives to slow leaks on cars over 100,000 miles. But frankly, if your objective is to save $, rather than using expensive oil and stretching the interval, you’re better off using cheap oil with a shorter interval.  Walmart and Costco’s store brands are fine, as is Amazon’s and the auto part chain’s (O’Reillys, Auto Zone). As long as it’s API certified. 

Oil cheap, engine expensive. Change it every 5k miles or yearly, if you mainly drive short distances with lots of stop start driving, twice yearly or every 3k miles.

I think that's too long of an interval. It's risky no matter what oil you use, because it gets harder on the engine during cold starts. Use an oil that meets the specs in your owner's manual, and change it more often than that ... at least twice as often.

I would suggest a high mileage type oil at the proper viscosity for the ambient temperature and a filter and PCV valve every 3000 miles, max.