Can the iPod touch be upgraded to ios 15?

If your iPod is a 6th generation model as suggested by the signature strip in your post, then no, it cannot update to iOS 15.

You can confirm which model you have, by looking in Settings/General/About, which will tell you which version of iOS is currently on the iPod (under the Software Version heading) and the model type (under the Model Name heading). On my 6th gen model, the Model Name states iPod Touch (6th gener... and then cuts off.

A 6th generation iPod Touch can receive updates (if there are any) but not to iOS 13 or later. If you look in Settings/General/Software Update, that will tell you either that your iPod is up to date, or that there is an update for it in the iOS 12 range.