My realm lags!

So for 1 year and 9 months (i think) my realm is having so much lag and we do have an idea what it's caused by. The lag just teleports players back a lot and we think the 1.9 update wrecked it because in 1.8 the realm wasn't laggy at all. It takes a while to join the realm and the lag only occurs in 1 world and not the other 2. I have tried downloading the world to singleplayer and it crashed Minecraft.When Minecraft has an update it makes the lag worse now it's at the point when someone/people have been on for too long you just get timed out. Every time I back up the realm it says a error has occurred but the backup works. We know by far it isn't caused by command blocks because we have tested it out when command blocks weren't on as a experiment, we searched the realm if there is any lag machines and we couldn't find any, me and my friends internet connection is fine and the lag occurs to every player who is on the realm and it still lagged and my friends don't want to reset the world at all. It also takes a long time to join the realm. Can anyone help me resolve this?