Just for everyone's information - there is a bug in Chromium engine where a sound played at a position (to give a stereo effect) causes a huge jank the first time it is played. I have created a bug report in chrome here as this is not directly a c2 problem; the problem appears on Chrome and nw.js...
To work around it, play a quiet sound at an object during your start/splash screen and all should be well thereafter. I'll post here when the problem is resolved.