OCI's will highly depend on application, oil quality, air filter quality and oil filter quality. Some oils have additional additives that prevent breakdown of various special lubricating agents, while others don't. Some oils have additives that improve protection against carbon contaminates, others don't. Even within the realm of synthetics. I tend to run AMSOIL signature series only in my cars. I've had good luck with it in my Focus, even with extended 15,000 km to 20,000 km OCI's.
I just did my first oil change on my 2014 Mazda 3 with AMSOIL Signature Series 0W-20 and their synthetic filter. I plan to do oil testing to see where things are at down the road.
This is a little anecdotal, bit what I did find with Mobile 1 synthetic (my previous go-to oil), after about 5000 km, maybe 6000 km, I would do an oil change and then the engine would "feel better". Almost smoother. This could be in my head for all I know, but I didn't experience this when using AMSOIL. Even after 20,000 km, I would do a change and the engine didn't feel any different, as if the oil I pulled out was still doing its job admirably. Take that for what it is. Anecdotal, and with no quantifiable data to back it up really. I did put over 250,000 km on that car though before getting the Mazda.
Right now, I set my maintenance computer for 15,000 km with the AMSOIL fill. Based on the oil and filter combo, I should be able to do 25,000 km. I'll do an oil test at or near 15,000km on my next oil change to see if it would still be good to go longer.