Hi Orrakull,
Thanks for posting. I understand GarageBand is taking a while to load, and I'm glad to see how I can help.
To clarify, which macOS version are you using under Apple menu () > About This Mac, and which Mac model do you use?
Do you see similar issues with any other apps?
Are you saving your GarageBand projects on your internal drive, or an external hard drive?
As a starting point, you might try these tests in order to narrow the issue down. This will help to rule out certain software causes and to determine if the issue is system-wide or user-specific.
First, try booting into safe mode: Use safe mode to isolate issues with your Mac. Once you boot into safe mode, try it out and then click Apple menu () > Restart once you've tested GarageBand and test again.
Next, create a temporary administrator account and open GarageBand there to see how it works: How to test an issue in another user account on your Mac
Once you've tested, feel free to reply back here with the results. Take care.