If I install IOS 15.1 on my iPhone 7 will I be able to receive 5G?

To expand a bit, you can't put iOS 15.1 on your iPhone 7, only iOS 15.5. But, that still won't get you 5G because the iPhone 7 doesn't have the hardware required to connect to a 5G network.

No only on 12, 13, & SE 3rd generation.