new tank setup

[kafug]

I was just wondering if anyone had some tips for switching tanks. Ihave a little 15 gallon setup right now but im starting a 94 gallon. Will i have 2 let the new tank setup for a long time or can i just start using the water out of my 15 gallon ever time i change the water and mix it in with new saltwater? An tips two make this a little easier would be great. And same thing with me sand can i just mix it in with new sand? I'm new at the whole saltwater thing so i don't know much