i want ios 13 not 15

It doesn’t support it… This is the umpteenth time today, that someone has tried to ask about updates for their iPhone 6. Please make use of the search function.

Is your device compatible to update to the new version? See the article(s) below. 

IOS 15.1.1 Compatability

IOS 15 and iPadOS 15 Compatible Devices.  *

iOS 14 and iPadOS 14 Compatible Devices.  *

iOS 13 and iPadOS are compatible with these devices - Apple Support.  *