Why raw images opening so slowly on Fedora (I tried KDE and Gnome)?

This is a forum, not paid support.
Waiting only a few hours then bumping your own post is bad form and wins few friends.

One thing you might do to improve your chances of assistance would be to include all the important data.
What version of fedora are you using?
Is it updated?
What app is being slow to load the image?
System specs?
What is a “raw image”? What format is it in? png? jpg? gif? or?
etc.

The more relevant information you may provide the more likely someone may be able to assist.
From the Start here category the Welcome to Ask Fedora! Please read me first! topic shows this about asking for assistance.

 You should try to make things easier for others that try to help you.
In general:

Check to see if the information you are looking for is documented on in the Fedora documentation 28.
quick-docs 28 provide lots of short one page step by step instructions on how to do many things.
Search this forum before you post: someone may have asked the question before, or experienced the issue before you.
Always mention the version of the Fedora OS you are using.
Try to clearly document what you were doing, step-by-step if you can.
Provide as much relevant information about your system
Commands that tell you about your system, its hardware, its packages and so on are documented here 34.
Don’t worry if you can not gather more information, though. Other users will ask you what what they need, and you will learn in the process too!