Why does my iPhone 15 Pro keep losing Wi-Fi connection?

iPhone 15 Pro: i cant recall how many iPhones i have had but this is the first time i would genuinely consider a competitor product. The wifi drops out constantly. Its slow. It loses connection. Like, constantly. Then with phone calls, it just drops them all the time. It’s not coverage of either wifi or mobile. In my house we hsve 5 iPhones, 2 iPads and 1 iPod. This iPhone 15 is the only device that seems incapable of maintaining connection. Have followed all the youtube tips, constantly resetting the thing, turning airplane mode on and off, turned 5G off, but nothing helps it. Absolutely useless and waste of money purchase

[Edited by Moderator]