How to transfer music from my old iPhone 4 to iPhone 6s Plus?

How to transfer music from my old iPhone 4 to iPhone 6s Plus? - 1

Hi you still need to use i tunes to do it.

Use iTunes or sign into your iCloud account on your new phone and sync your itunes purchases.

Assuming the music was purchased from iTunes, could use iTunes to sync them across. Either way using iTunes to do a backup of the old & restoring from the backup on the new is what you do