The point needs to be made here that even oils referred to as 'conventional' are not just 100% dinosaur rot. Kia Canada has a national account with suppliers in every dealer's markets to supply a "synthetic blend". We have Quaker State here, and I'm sure that if you check with your dealer you'll find they use a "semi-synthetic" oil which is truly the best of both worlds.
As for the rather large difference in oil change intervals, Canada as a whole is considered "rough service" or "extreme" environment for vehicles so our fluid changes in general tend to happen more often with all manufacturers. In Alberta we'll see -40F this winter, and nearly 100F in the summer, so yeah... we need to be a bit more diligent with our fluids.
Synthetic or not, a good way to tell if you're overdue for an oil change is to simply pull the dipstick and look at the oil. Does it look caramel coloured and can you see the stick behind the oil? Or is it so dark it's like black paint on the stick?
This is a perfect example of "good and not-so-good".
The top one is from a 17,000 km engine with about 3,000 kms since it's last service. The bottom one is overdue, period. Doesn't matter how old the engine or oil is, it's been too long.