Is it worth time converting Access query to T-SQL query
To me 30 queries does not sound like to much work in order to obtain the level of performance increase you will see having SQL Server do the work instead of Access. Especially if the data is going to expand to more users and is a more mission critical type thing.

Something you might consider is running your Access database through the SQL Server Migration Assistant for Access tool. This tool will actually move your queries to SQL Server. You can find more information about the tool here: Access to SQL Server Migration: How To Use SSMA