Can I get a 15.0 software update on an Iphone 6 Plus?

No, because it’s the iPhone 6 Plus. It really isn’t that hard to read the Apple website: iOS 15 – Apple (UK) (Bottom of the page). iPhone 6 Plus doesn’t have enough RAM to run anything iOS 13 and later, the most current software available for it is iOS 12.5.5. iPhone 6 Plus was released in 2014, and is obsolete.

No. It's not capable of 13 or above.

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Niel wrote:

No. It's not capable of 13 or above.

then why is iPhone 6 Plus listed as compatible with iOS 15.2 in apple's documentation?

iPhone models compatible with iOS 15.2

sorry, never mind. i just noticed it's the 6s Plus in the list, not the 6 Plus.