How to update iPhone 6s Plus to iOS 15?

OP wrote:

IOS 15.0 is available for my 6s+ iphone, yet the software update tells me 12.5.4 is up to date

Here at iPhone Software Update show too Your iPhone software is up to date.

But scroll down a little bit, will help to see the option to update to iOS 15.

Raicya wrote:

Sorry.

It is possible to update iPhone 6S Plus to iOS 15.

Here's an iPhone 6S just updated to iOS 15.

iOS 12.5.4 is the latest iOS version for iPhone 5S , 6 & 6 Plus.

I believe Niel's point is that if the phone shows as up-to-date with iOS 12.5.4, it is not, in fact, an iPhone 6S series but a 6.

Raicya wrote:

OP wrote:

the software update tells me 12.5.4 is up to date

And what that means is that the OP has an iPhone 6+, not a 6S+. The OP is apparently mistaken about the model phone they have.

People being mixed up about whether they have an iPhone 6 or 6S is actually quite a common issue. It's also one that, since the release of iOS 13 has mattered a lot. So, whenever you see a question where someone says they can't update their iPhone 6S past iOS 12.5.4, have them verify the model. It will save you both a lot of time.

An unit running 12.5.4 isn't an iPhone 6s Plus or capable of 13 or above.

(205094)

Sorry.

It is possible to update iPhone 6S Plus to iOS 15.

Here's an iPhone 6S just updated to iOS 15.

iOS 12.5.4 is the latest iOS version for iPhone 5S , 6 & 6 Plus.

This is OP question.

Go to Settings>General>About>Model Name. What does it say?

Did you actually READ the post from IdrisSeabright? An iPhone 6S cannot possibly have iOS 12.5.4 on it, so it isn’t a 6S.

IdrisSeabright wrote:

And what that means is that the OP has an iPhone 6+, not a 6S+. The OP is apparently mistaken about the model phone they have.

That's possible, nobody is perfect.