Reproduction steps:
1. Open the attached project named Case_1181342
2. Open the Grid Prefab Asset in Prefab View
3. Paint or Edit the Tilemap in Prefab View
4. Save the changes (either using the Prefab Save button or Auto-Save)
5. Notice the time taken for the frame to save the changes
5a. Using the Profiler in Editor Mode is one way.
6. Switch to Asset Pipeine v1 in Project Settings -> Editor -> Asset Pipeline -> Mode -> Version 1
7. Save and reopen the project for the setting to take effect.
8. Repeat 2-5 and see the time taken.
9. Create a Cube in the scene and convert it to a Prefab
10. Repeat 2-8 to see the time taken in saving changes to the Cube Prefab between Asset Pipeine v1 and v2.

Expected result: There should not be major differences in performance between Asset Pipeline v1 and v2, especially when Auto-Save is enabled in Prefab View.
Actual result: Asset Pipeline v2 is slower in saving Prefab changes in Prefab view compared to Asset Pipeline v1 with the same Prefab Asset

Reproducible with: 2019.3.0b8, 2020.1.0a13

Notes:
1. When saving Prefab changes in Prefab view, Asset Pipeline v2 redraws all the active Editor Windows compared to Asset Pipeline v1, even though some of the Editor Windows are not affected by these changes (eg. Audio Mixer window). Asset Pipeline v1 only updates a subset of the Windows, which are the ones affected. Redrawing of these Windows contributes indirectly to a significant increase in the frame time when saving the Prefab asset.