At the ZX14 forum I read that the valve check interval is 15K in the U.S. but more like 25K for bikes sold in Australia, Malaysia, etc. Apparently, the longer intervals have nothing to do with the fuel and the engines are identical.
Have you considered 25,000 km is approximately 15,000 miles? Could that possibly have anything to do with it?
Australian roads are measured in km.
2018 F-150 XLT SuperCab 4x4 2.7L
2016 Beta 430 RS
2016 Subaru Outback
2013 Tesla Model S 85
2009 Husaberg FE450
1983 Porsche 928S