Unable to set iPhone 15 to vibrate for all notifications

Settings > sounds & haptics...

check under each alert situation: {ringtone, text tone, voicemail, new mail, etc}

Choose one and then scroll UP to Haptics.

Be sure you have actually selected a haptic to play in that alert situation.

Note: "Default" in this context is not a haptic, it is OFF

"Alert" is just one single vibration. That is easy to miss..

try something interrupted, and longer duration.

Further down the list -- haptics like Rapid, S.O.S., Staccato, Symphony.

Also, when you select one, it should play for you, else your haptic engine might be broken.

Have you tried force restarting the phone?

Force restart iPhone - Apple Support

ETA: Grant has probably hit upon it. However, if he hasn't, my next question would be are you also wearing an Apple Watch?

kennykopter wrote:

I don't wear an Apple Watch. But I do wear a North511 Nexus Pro Smartwatch; which does blue tooth to my iPhone. I get emails on it. But only visual notifications. No sounds or vibrations. Should I look into my documentation for it?

Another brand of watch shouldn't have any effect, at least not to the best of my knowledge.

kennykopter wrote:

Since my watch does get text and email, can you suggest what I might do to determine if it's interfering and how I might fix it?

Unless it's an Apple Watch, it shouldn't interfere at all.

Settings>Sounds & Haptics>Ringtones and Alerts>Haptics>Always Play