I can’t update app on my phone and i need iOS 15.0

Hello,

There are different ways to ensure the highest iOS that your device will support is installed on your device. For an iPhone 6S or 6S Plus that's iOS 15.7.8

This support article has instructions about updating an iPhone or iPad wirelessly —> Update your iPhone or iPad - Apple Support

You can also use Mac and PC computers to update system software, as described in this article —> Update iOS on iPhone - Apple Support

When updating, your device will update to the highest version currently available that it will support, or it will just say it is up to date (and can't go any higher) and won't install anything. If you want to run a higher system version than your current device will run, that you need to buy a newer device.

Hello Candy in order to update your app that is saying you need iOS 15 or higher you need to go into your settings and click on general from there click on software update which is right under about and see if there is a update available on your device if there is click download and then install but make sure you have enough storage for it to download & install. Hope that helps!