Well, first thing, 4 into 1500 is 375 ! It would leave you with a small spool of line.
I would load the 375 on one reel then fill it up with some backing of whatever, then respool to one of the other now reels, this will put the backing on the bottom of that spool . Now you will have a full spool with braided line on top. Repeat for each new reel, and on the last you should know by now how far to fill the last spool with backing.
Good Luck, and have FUN !