World conversion crash at 97% or higher (takes hours to load)

When transferring a world it takes hours to load and just as it hits 90 some percent it crashes my game. I reported my world to Mojang a while back, but I don't know where to go with the receipt number.
( I know this is a common issue but everyone's case seems different)
Feedback is what I'm looking for from anyone who has solved this issue, please and thanks.