Can I create a backup of an old iphone? upgraded recently

Hello!

Recently upgraded from a 3GS (yes yes, it was old) to an iPhone 6. However, It wasnt until after I left the store that I realized that I didn't have a recent icloud backup. It looks like all the info loaded from only November of 2014, and nothing after that. Is it possible to create a new icloud backup using my old 3GS, so that I can restore that backup to my iphone 6, so all the info from 2015 is there? (even though i guess that sim card isnt "active")