I see you are comparing 9.2 and 9.4 -- if you were not already aware
there is a kernel restriction on shared memory on Linux systems which,
if I recall correctly, must be adjusted in versions before 9.3...
https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server#shared_buffers
Not saying it's the answer but maybe another thing to look at...
All the best
Peter
