Reproduction steps:
1. Open a new or existing project
2. Install DOTS Editor preview.2 - 0.1.0 (Unity versions 2019.3.0b11 and higher)
3. Make sure no Object in Hierarchy is selected
4. Enter Play Mode and enable Stats
5. Observe current performance and select an Object in Hierarchy with Inspector window visible

Expected results: performance stays relatively the same
Actual results: performance drops around 10% - 20%

Reproducible with: DOTS Editor preview.2 - 0.1.0 (2019.3.0f4, 2020.1.0a18)
Could not test with 2017.4; 2019.3.0b10 - no DOTS Editor preview.2 - 0.1.0

Notes:
1. you can actually see that Inspector is being updated between very small intervals of time (try moving an object in Scene view) compared to without JOBS Editor package which is likely causing the performance to drop
2. The first version to support DOTS Editor preview.2 - 0.1.0 is 2019.3.0b11