World Overrode after updating to 1.15.1

Put the summary of the bug you're having here

What I expected to happen was...:
The world version to be able to be different without problem.

What actually happened was...:
Upgraded world to 1.15.1, then wanted to change to modded 1.14.4. After loading with modded 1.14.4, world was like it was new, house and animals were gone, but things in inventory were still there.

Steps to Reproduce:
1. Make world with 1.14.4.
2. Load world with 1.15.1
3. Load world with forge 1.14.4-28.1.108