Query execution time is random, need to identify the root cause
In general, A primary key constraint creates a clustered index in the table. It's important has at least one index in the table to avoid fullscans.

As you said the table doesn't have any kind of index, nevertheless you're searching in the table with a predicate which has two columns. In my experience, I'll create a non-clustered index to support this query. There's another essential thing, you should include all columns that you're using in the statement select. Include columns are not key columns in the index, soo be careful.

CREATE INDEX idx ON MyTable (column2 ,column3) INCLUDE (Name, Address)


I've already read a lot of pages of this book and I recommend it for you.

Expert Performance Indexing in SQL Server

This another one here is good too.

SQL Server 2017 Query Performance Tuning: Troubleshoot and Optimize Query