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)