iOS 15.5 install issue on new iPhone 12

[Kellyad]

We have upgraded our 2 phones from iPhone 11 to 12. Put the sim from one Iphone 11 into the 12 and transferred everything over from 11, but had to do an iOS 15.5 update first on the 12 which took 2 hours. 
Then put the sim from second iPhone 11 into the other 12 and iOS 15.5 has to be done first again. But it is just stuck saying 12 hours remaining? Why?!

[Chris_B]

@Kellyad   Because it has to download iOS from Apple server to install on your device and then it has to installed it on the device after its downloaded it.      You could try restarting the device if you have any other issues with it you’ll need to speak with Apple it’s their OS bring installed on their device. 

[Kellyad]

Thanks Chris I restarted and it’s finally completed ✅