Performance of packaged workbooks is not dependent on the internet connection unless the packaged workbook file being accessed is from a shared directory or Tableau server that relies on internet speed.
If thats not the case and assuming the file is local and machine(laptop) is same, the reason may lie in the CPU usage at each time (high usage slows all processes).
Hope its one of the two but I'll definitely try to validate that soon.
Hi Michael Rudis,
Internet speed would not be a concern if the packaged workbook is stored on your local machine and if the connection to your data source is a extract connection.Why use Tableau Data Extracts | Tableau Software .
You can refer to the following articles to improve performance and record performance of your existing dashboard.