You don't have to use Mobil 1. Any 5W30 oil which is dexos1 certified will keep your warranty alive and happy.
As for which oil is best, well, let's not open up a can of worms.
15W50 is not DEXOS certified at all (but it will not void your warranty)
I keep 15W50 in my car year round because it's a track car 90% of the time and 10% street driven.
If your location gets cold I would recommend swapping back to 5W30 during the colder months.
15W50 is only really bad for cold starts and driving around before its up to temp but once it warms up its fine.
you'll experience a little higher pressure & oil temps with 15w50 but it's not a problem.
If you don't track "often" I wouldn't worry about using 15w50 at all and stick with 5w30