Background:

https://db2indocker.blogspot.com/2015/04/db2-do-not-start-in-un-privileged.html

The main reason behind this is that DB2 needs larger shared memory segments. By default, Linux containers get shared memory segments of 32 MB in Kernel Versions less than 3.16.
In kernel versions 3.16 and above this issue has been addressed and Linux containers get much larger shared memory segments.
That’s why we add —privileged=true parameter when running it.

Kernel 3.15 went EOL in 2014, so this seems like a workaround that shouldn’t be particularly necessary - if it’s just for the reason cited in that blog post.