Hi there Jackcbr,
You can customize notifications to your liking by going to Settings > Notifications > Messages (if using the Messages app). On the bottom of the screen after tapping Messages, you should see "Customize Notifications." In there, you can set up Repeat Alerts which means the notification will make a sound every 2 minutes for the chosen time (once, twice, 3 times, so on). There is no setting to make it louder or longer than other notifications.
Another thing to consider, is to possibly change the tone for texts on your iPhone, which can help distinguish text messages from other app notifications. You can do this in Settings > Sounds & Haptics > Text Tone. You could also set a specific sound for a specific contact as seen below:
"Assign a different sound to a contact
- Open Contacts, then select a contact.
- Tap Edit, then tap Text Tone.
- Choose an option below Alert Tones.
- To allow alerts for messages sent by this contact even when Do Not Disturb is on, turn on Emergency Bypass."
That information, and more, can be found here: Change message notifications on iPhone - Apple Support
If none of those choices suit what you are looking for, you can submit any feedback you have with this link: Feedback - iPhone - Apple
Take care!