Steps to reproduce:
1. Create a new project
2. Import Standard Assets Image Effects package
3. Add several Image Effect scripts(e.g. at least Bloom, DoF, Twirl, Vortex, Sun shafts...)
4. Enter Play mode

Expected result: quick enter into Play mode
Actual result: the first launch takes a relative long time to load, following launches enter play mode quickly

Reproduced on 5.4.5p1*, 5.5.2p4, 5.6.0f2, 2017.0a4 on Windows 10
Not reproduced on OSX
*5.4.5p1 load times are slightly better

Notes:
-This behavior resets on every restart of the system, may be required to do so once scene is set-up (cant be cached effectively)
-Not post-processing related (general shader compilation)
-Reproducible with other effects packages besides the Standard Assets(e.g. Post-Processing Stack)