If you plan to keep it four years or so then you can stick to the schedules safely. If any problems arise during that period then new car warranty will sort it all out.
The greater likelyhood of having engine oil related problems is more likely to raise its head when the car is getting older.
The makers like to advertise these long service intervals, it's good marketing policy and suits the fleet and contract lease markets very well.
20,000 is a bit long in my estimation, particularly with turbocharged engines, which do load the oil with high temperatures and other stresses.
With any turbocharged car it's very good practice to let the engine idle for a minute or two before pulling the key. This is worth more than you imagine.
If it were mine, which it isn't, and unlikely to be so because I'm not a great Vauxhall fan, I'd consider an interim change at 10,000 miles but using a good quality synthetic oil.