Fully synthetic oil will reduce or eliminate sludge deposits ,i.e. cleaner engine overall for the life of the engine. tHat's a plus to me. But I keep intervals at 4- 5k miles. Mobil 1 i've used since 1977. Note , the New Mobil 1
Extended Performance oil does not meet Toyo specs just yet. I would not use it even though it claims intervals of 15k mile s. Use the standard Mobil 1 .(5w30)

I always keep to Toyo recommendations anyway.