oil filter

I am currently using 15w-50 with mobil 1 gold cap. I am interested in switching over to AMSOIL. Can I use 5w-30 or 10w-30 seeing that the oil is superior to the Mobil 1 stuff. I always feel like the 15w-50 is too thick for the car not that i've had any problems with it at all. What do you...