If it's the SQL Server queries causing the delay, the key for slow queries is not the complexity. A very simple query can take a lot of time. Two main things to investigate
- Do the queries fetch unnecessary data. You went through the columns but how about the rows?
- Is proper indexing in place. Look ate the WHERE clauses of the problematic statements do you have indexes that provide quick access path to the rows, taken that your only fetching a small portion of the table
- Use Tuning advisor to see what recommendations the database has, see Start and Use the Database Engine Tuning Advisor - SQL Server | Microsoft Docs