Is it going to destroy my phone

Is it going to destroy my phone

No.

iPhone 6s, iOS 14

You can update your iPhone to iOS 15.7.1.

If your iPhone is eligible for an update, you can check by reading this Apple article:

iPhone models compatible with iOS 15.7

iPhone models compatible with iOS 15.5 – Apple Support (UK)

Go to Settings -> General -> Software Update -> Download and Install.

You need about 6 GB device storage and good Service & Wi-Fi.

If they are On, turn Off Hotspot & VPN.

Charge the battery > 70%.

See the following Apple articles:

Update your iPhone, iPad, or iPod touch

Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If your iPhone, iPad or iPod touch won’t update

If your iPhone, iPad, or iPod touch won't update - Apple Support

You can do the update via PC, see this Apple article: Update software on iPhone, iPad or iPod touch in iTunes on PC

Update software on iPhone, iPad or iPod touch in iTunes on PC – Apple Support (UK)

If you have a Mac see this Apple article: Update your iPhone, iPad, or iPod touch with the Finder

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

iOS 16 will not destroy your iPhone 6s. In fact, your iPhone cannot even go that high. It is an older phone and can only update to 15.7 … which will also NOT destroy your phone.