Fix the issue with speed. email app that comes with the phone is able to download and open the email before outlook even fires up.
I did a test where i sent an email to both my work and gmail account from my work email, waited until i got the notification on both and clicked & timed the events. Responding to an outlook email takes about 4 times as long as responding to gmail. In the almost 8 secknds it took outlook to open, i had already read the email on my native email app (not gmail).

Hi there,
Thank you for using Outlook and letting us know about your current experience. We really appreciate your support.
We are so sorry this is happening to you. Our helpful colleagues over the in-app support are more than happy to have this answered. Please contact us through the Help Section of the app (in the Settings) so that we can assist you in the best possible way.
We look forward to fixing this for you.
All the best
The Outlook Mobile Team
PS: Please use the Help Section of the app for any questions, we are not able to see replies to this address.