Steps to repro:
1. Open attached project
2. Enter Play Mode

Expected result: Editor takes 1-2 seconds to enter Play Mode (like in 2018.2)
Actual result: Editor takes 110+ seconds to enter Play Mode

Reproduced in: 2018.4.0f1, 2019.1.2f1, 2019.2.0b1, 2019.3.0a2
Not reproduced in: 2018.3.0a2

Note:
1. Entering Play Mode second time is way faster.
2. The project contains several thousand Tilemap tile assets, removing these from the project drops the first time Play Mode startup time significantly.
3. Profiler shows "enterPlayModePreWaeake.Invoke takes 114904ms, on the second play it takes only around 4.