Chrissy LeMaire explains ways that the dbatools team reduced how long it takes to load their module:
We noticed that the longest part of importing the module was importing all the extra SMO DLL’s that we require for many of the commands. We import about 150 DLLs and it looks like that number will only grow as we begin to support more functionality (such as Integration services, etc.)
To address this concern, Fred added multi-threading via runspaces to our import process. Too cool! This resulted in a significant decrease in time.
Read on for more details; some of these tips might work on other slow modules, too.