Please note: 4 year old thread.
Also, ad-hoc queries and plan cache has nothing to do with sleeping connections. Sleeping connections are ones waiting for input from the application, they are doing nothing.
Max degree of parallelism has nothing to do with sleeping connections, nor with plan memory
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability