How often do you change the oil in your car. I have always had it done annually when serviced, but I see some people online recommend every 3,000 miles, which doesn't seem very far at all to me.

I do mine ever 6000

Depends which engine but for a 2015 car I'd be sticking with the recommended intervals anyway.

If it's a fussy engine known for oil issues like pump failures or carbon deposits (1.6TDCi 16v) I'd do 6k changes.  Normal engines without oil issues I'd leave 10-12k or yearly...unless it's on longlife in which case you can leave it 20k or so.

Unless it's a race engine, 3k changes are just a waste of money and not great for the environment either.  

I lived in the USA for five years (2006-2011) and owned a Mk1 Focus which I bought new.  The recommended interval was 3 months or 3000 miles.  At the time I didn't think this was unusual as this was my first car!  One of my friends visiting from the UK pointed out that four oil changes per year was probably three too many,.  However, they only cost $25 (at a Ford dealership) and for that they also rotated the tyres, checked battery performance, topped up all fluids, washed/vacuumed the car and gave me free coffee and pastries if I waited, or a free ride to/from work if I didn't.  I really couldn't complain!

Yeah, to be fair I have mainly seen US YouTube videos recommending 3,000 mile oil changes, so maybe it's more of a cultural thing than an engineering thing? After all, they have some of the same cars, same engines, same oils etc. 

I watched a good video on Mobile 1's 20,000m oil, which is significantly longer than 3,000m! It wasn't a sponsored video, but they went behind the scenes to see the R&D that went into it, the accelerated testing, a pick-up they put on a dyno for 500,000 miles, changing the oil and filter ever 20,000 which was quite impressive. They also own a fleet of taxis in Las Vegas that they use as test beds for real world driving.