Why does it take so long time to insert stored procedure into a hashtable?

I have a stored procedure, MySProc, that takes 7 seconds to execute.

I have made the following stored procedure, MySProcWithWhereClause, where I simply just want to have the table from MySProc, but with an extra WHERE clause on it.

Here it is:

CREATE PROCEDURE MySProcWithWhereClause
BEGIN
    CREATE TABLE #temptableT 'params'

    INSERT INTO #temptableT
        EXEC MySProc

    SELECT * 
    FROM #temptableT 
    WHERE param1 = param2

    DROP TABLE #temptableT
END 

However, this stored procedure takes ages to execute. I waited for 2 minutes and decided I need another solution.

Why is it so slow, and is there a faster way?

I checked out other questions, for example this one, but it did not give me a proper solution.