Steps to repro:

1. Open attached project in Unity 5.4 on Windows;
2. Open 'test' scene;
3. Launch the scene, observe and remember FPS and frame time numbers in the left corner of the screen (see attached 5.4 screenshot);
4. Save project and close Editor;

5. Open Unity 5.5;
6. Open 'test' scene;
7. Launch the scene, observe FPS and frame time numbers again.

Expected result:
FPS should not decrease significantly and frame time should not increase significantly.

Actual result:
FPS decreases and frame time increases by about 50% comparing to 5.4 (see attached 5.5Actual screenshot).
Regression introduced in Unity 5.5.

Notes:
- Reproducible in 5.5.0b8;
- Not reproducible in 5.4.1f1, 5.3.6p6;
- Reproducible only on Windows 10 (high-end machine);
- Not reproducible on OSX 10.12 (low-end machine);
- Also happening in standalone builds;
- Performance drop is not reproducible in Standard Assets 'Car' scene; seems to be specific for SpeedTree project.