When profiling the Editor in 2020.1, a <callDelay> section appears highlighted in editor play-mode that causes a laggy experience in editor.
Attached -photos and recording of side by side profiling of entering play mode for both 2019.4 and 2020.1

Repro steps:
- download this project
- turn on editor profiling
- enter play mode
- after that, pause and scrub the timeline and notice that <CallDelay> take up 89% of the CPU on enter play mode.

For more complicated projects, that delay is really really large, as these forum posts suggest
https://forum.unity.com/threads/editor-loop-high-thread-utilization-on-play-mode.899840/
https://forum.unity.com/threads/2020-1-0b11-unresponsive-and-extremely-choppy-in-play-mod.906608/

Not reproducible in 2019.4 or 2020.2.0a14