Why does AttachDBFile make everything slower?
You are comparing two different servers. Likely different hardware specs, possibly different versions. Possibly even querying different data. Apples and oranges. The attach is probably a red herring (there is a cost in attach and querying cold data, but will amortize over many queries. You do measure hot cached and repeated runs, don't you?)

Read How to analyse SQL Server performance to root-cause the performance problem.