My husband forgot his password on his iPhone 15

There's a difference between between a passCODE which is a four or six digit code used to unlock a mobile device after you turn it on (or other services on a mobile device), and a passWORD which is what is used to log into your Apple ID account which may be required in resetting a forgotten passCODE. I am not clear as to which you are referring.

Read the Apple Support document for what to do if you forgot the passCODE on an iPhone or iPad. Click here then select your device type if necessary --> If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support - Which one you can use depends upon your equipment configuration.

Also:

If you forgot your iPad passcode - Apple Support

Either method will require erasing the phone. He can, however, restore it from a backup. If he does not have one then this is a learning opportunity.

Read this support article for what to do if you forgot your Apple ID passWORD - If you forgot your Apple ID password - Apple Support

or go directly to this link --> http://iforgot.apple.com/

If you still need help this page provides country-specific Apple Support contact information ➞ Contact Apple for support and service - Apple Support