Reproduction steps:
1. Open project attached (SekaiTabi.zip)
2. Go to Assets -> Sprites.
3. Select 2D Textures (ThePerfectGalaxy*) while holding Ctrl.

Expected result: Sprites are selected without any lag and other problems.
Actual result: It is hard to select sprites, Editor starts lagging. Might even cause a crash on very low-end devices.

Reproduced on: 5.3.0f4, 5.3.7p2, 5.4.0f3, 5.4.3p3, 5.5.0p1, 5.6.0b1.

Note: it is easier to notice this problem when using big (over 5 MB) 2D textures.