The way business logic in the system is currently designed , there are no 'common ones', except for some ids (already indexed) used in other process rather than this dynamic filter.

Based on that we also evaluated the approach of using something else like druid [1] [2] that is built for reading performance, but I am still studying possibilities and have no idea about the impact and problems a change like that would impose.

[1] http://druid.io/

[2] https://metamarkets.com/2014/building-a-data-pipeline-that-h...

Another thing to note is that Mongo is simply very slow. Without indexes, something like Postgres is much more likely to be fast.