I've seen simple things help such as setting the date/time in the TV to changing the DNS and updating firmware. Set aside time to call Samsung on this and be sure to have them walk you through these basics. If they can't resolve then you have grounds for a return+refund.
I have a brand new Samsung UN65KS8000 UHD tv that has slow wired and wireless networking. Both HD and 4K content constantly buffers with warnings of slow internet speed. I have 50 Mbs fiber service and all other devices see nearly that speed but apparently not the tv on either wired or wireless. The router is on the same stand as the tv so signal strength is not a problem and the buffering happens even when no other devices are active on the network. There appears to be no way to see what speed the tv thinks it is seeing as I cannot find any tv settings that would allow one to see that info. Software update is listed as current. I cannot believe Samsung would put out a UHD tv that is essentially useless for networking even in HD, so what else could it be?