when I rooted my devices I accepted many risks. it seems 15MB is the threshold. the low storage warning won't kill installs, and is set for 10% of whatever storage your device has. this can be 15MB, 150MB, even 1GB depending on capacity. I have discovered the package installer (a system app in all versions of Android) is what throws the 'insufficient storage available' and Google Play just uses that on its own. it does not have its own installer. even the installer built into rooting tools like ES File Explorer and Root Explorer do the same thing, although the message is different (out of space, install failed, etc) but for the same reason. if I get 1MB more, say it now sits at 16MB, it will install at least apps not going over that 1MB. even if it reports 15.24MB left, a 50KB app will install. the 15MB is the limit for the package installer. and it affects all installers, so there must be something the installers are looking at to determine that. the installer exits, based on that variable.
and as for the ANRs, since there is a developer option to turn them on or off for background processes, the means must exist to do it for foreground as well...at least, it seems possible.
I CAN install apps by copying them to /system/app which has a different amount of free space for some reason, and they auto-install on a reboot of the device, and show up in the list of installed apps afterwards. I think this is how system apps and bloatware get installed by some parties. but the same trick, manually copying the APK file to /data/app won't achieve the same result. the file will copy successfully, but it won't install on a reboot. I am not sure if this is a simple permissions issue or not, either.
Samsung Galaxy Note 3 (rooted, HyperDrive ROM)
Samsung Galaxy Tab 3 7.0 (non-rooted, stock)
Samsung Galaxy Tab 2 10.1 (obsolete, slow, rooted)
Samsung Galaxy Note 10.1 2014 Edition