I will give this some more though. Each form I have is part of a module of the application logic.
So I thought it would be recommended to split them into DLL's or more experienced programmers would split the forms at presentation level too.
Maybe I will just leave it as it is, because it is working fine so far and I will write an update program that overwrites the entire exe file instead of particular DLL files.
10 forms is fairly small as apps go, I'd leave it in the single exe. It is usual to divorce the UI from the business logic and the database functions. I'd assume that all your business logic is in the code behind the form, this is usually extracted into a separate class.
Never underestimate the power of human stupidity
You could have chosen this[^] forum, or this[^] one. Richard is right - as your question doesn't have any code element, i.e. you haven't actually asked why your code is slow, then it's not for this forum. Your question is more general and, dare I say it, architectural.
*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington