memory per user

How much memory is being consumed by each connection ???
Is this is a constant for the OS or every database ???

Where can I find this ???

I hope it is 1.5 M for evergy session in the database level..

Do you mean the uga? You can check the uga for a given user by:

select value sess_mem from v$sesstat s, v$statname n
where s.statistics# = n.statistics#
and n.name = 'session uga memory'
and s.sid = (user id you want to check);