I searched the world over for the 15W-40 and the only one I can find locally is Shell Rotella T SAE 15W-40 API SL certified....which by the label seems to be marketed towards Diesel engines but I have heard of people using it in motorcycles.
I also found Castrol 10W-40 for 4-stroke motorcycles that is API SG certified.
Which oil would you use if these were the only choices you had?
Thanks
JC