Performance Tuning :: Collection Count High In Memory

I have two tables with same columns(15 of them), I am trying to find difference between two tables using minus operator and then insert in stage table using below code

Issue is table1 has 50 million records
table2 is empty

so when first time when we execute this v_collection1,v_collection2 collection will have 50 million records in it which will go in memory, I think this is not good, because going in memory will eat memory and resources while sorting and other activities ?

After fetching records in collection we are inserting that in stage table and then COMMIT so i think that wont be good because committing 50 million will generate large amount of redo?

below is snippet of my code

DECLARE
type lst_collection1
IS
TABLE OF table1.col1%type INDEX BY binary_integer;
type lst_collection2
IS
[code].......