This script will search all logged in users and return the spid along with the number of seconds since that spids last batch was executed.
One of the issues you'll face with SQL Server is blocking which is caused by other processes that are holding locks on objects. Until the locks are removed on an object the next process will wait before proceeding. This is a common process that runs within SQL Server to ensure data integrity, but depending on how transactions are run this can cause some issues. Are there ways to get around blocking by using different indexes to cover the queries that may be running?