It used to be that the oil change interval was something like 3k miles for stop-n-go traffic (or dusty conditions) - ie, regular city driving. You could go about 6-8k for highway driving. If you were doing off-road driving, the number could be as low as 2k.
Today's oils are better, and so is the manufacturing and other factors; so longer intervals don't surprise me - but you have to be dealing with a newer car, something made in this century at least.
Even so, for my own vehicles I try not to go much beyond 6k between changes, and for one of my vehicles it's closer to the 3k mark (because I want it to last as long as possible - then again, its engine is a known oil-burner, and between oil changes I add enough oil for it to equal an oil change; I could almost just change the filter and do nothing else). The money I may be wasting isn't a big deal to me, plus I get a fresh filter (also, I do my own oil changes, so the numbers are a bit lower depending on what dino juice I use).
Generally, the best way short of an analysis to judge doing an oil change is by looking with your eyes at the color of the oil, by feel (rub it thru your fingertips), and by smell. It's a thing you have to get a "feel" for, and between that knowledge and what your miles since the last change, you can know if you need a change or not.
Another thing you can do (I learned this from a website that tested an analysis company - and to see how long they could really go between oil changes) is to (every 3k) drain a quart of oil out of the engine (you need something like a fumoto plug for this), and then swap on a new filter and refill with a new quart of oil. It's basically a "topping up" procedure, but if you do that, you can go for about 12k between full oil changes. However, you should only do this if you are analyzing your oil.
Compare this to GM/Chevy vehicles where this is a 'solved problem' with their on board DICT computer, it measurements the containment (via resistance? electricity?) in the oil & tells you the 'health' or 'life' of the oil until you need to change it. This leads to a lot more reasonable oil change intervals in line with Mobile's testing over the years: 5k, 7k or 10k change intervals are common.
BMW is one of the few brands that recommends once a season, or 10k, because they know what oil is capable of, in so far as they've removed dip-sticks entirely (retarded decision, but hey). However, most dealerships & shops? They still want that sweet money on that 3k oil change. 5k has become the 'open secret' standard, though.
I'm talking about the "Service Required" indicator/message that appears in the central info display, not the "Check Engine Light". Two different things in the VW, Lexus, and Jeeps I've owned.
These days, most (all?) cars have an idiot light that pops on every 5-10k miles, based on usage patterns. Some have a more robust algorithm than others. Either way, in my experience, my last 3-4 cars (Jeep, Lexus, Volvo, VW) have all gone about 8k miles between services, as indicated by the light.