You can look at currently running queries as much as you like, but queries are not what use memory, and so you'll be wasting time looking at that.

SQL's memory usage is mainly the data cache and the plan cache, and both exist as optimisations.

Chapter 4 - https://www.simple-talk.com/books/sql-books/troubleshooting-sql-server-a-guide-for-the-accidental-dba/