IOS app takes 12-15 seconds to open. Using iphone 12 and latest OS and deleted and reinstalled app too.

Updating the iOS and reinstalling the QuickBooks Online mobile app is the best starting point to resolve the issue. I appreciate you for doing that, @DJO.

Solving the QuickBooks Online app takes 12-15 seconds to open, which is my focus here. Let's get your mobile app up and running by ensuring that your iOS version is 14.0 or later. Also, ensure that your internet connection is fast to avoid delays in opening the app. 

Once confirmed and the issue persists, I'd recommend contacting our Customer Care Team. They can examine the problem and send a ticket to our engineers for further investigation if needed. 

Here's how: 

1. Open the QBO app and click the three dots on the upper right side. 
2. Select Help, then Support. 
3. Complete the required information and submit the request. 

Ensure to call them within business hours to ensure a swift response. 

Check out these articles below to know the different features available on your device and get answers to the how do I questions in QuickBooks: 

• QuickBooks Mobile App FAQS
• QuickBooks Online app overview

If you have any further questions or concerns with QuickBooks, please post them here. I'm happy to respond and help you again. Just take it easy, DJO.