What type of oil to use in 2015 LS Sport?
 

Regular or synthetic?

Synthetic.

Factory specifies synthetic

always synthetic if you love your car :)

Synthetic, for all my current and previous cars.

Just to make sure it's clear, with this car it's not a decision to use synthetic "because you love your car", this car came with synthetic from the factory, 0W20 and requires synthetic for the factory oil change interval and maintenance schedule. Not using synthetic oil would likely be an issue for the warranty.

Synthetic and every 10k miles. :)

If it's a throw-away car (i.e. a short-term lease), feel free to fill it with cheapo "gas-station engine oil"...

...but then make sure the next owner of this LS can't track you down :)

If it's your car, of course nothing but synthetic would work.

I wouldn't do that on a lease either. They're within their rights to ask for maintenance records, not that they will, but they can. The small difference in cost over a lease is negligible, and plus its the right thing to do because its what you agreed to do in the lease.

There's also pesky things like honor, ethics and karma...

Ah yes..... KARMA. it's a ******

Don't want to down that road