I resolved my overheating issue which sounds very much like yours by lowering the water level in the radiator.
If one uses dishwasher detergent to clean the cooling system be sure and get the low sudsing type. Don't ask.
I overcame my overheating issue by loweriing he water level in the radiator, it was overheating after driving about 15 minutes much like you are reporting!
That's strange.