In reply to Juni. The selected delegates do not receive monetary aid from the society. They do, however, have centralized plans while at the convention. Bus, hotels, things like that. But, it is all paid for by each individual delegate. Sometimes the friends in a particular KH will get together and pool their money to send one of their own to the convention. This proves a spiritual boost for all involved.
Some do stick around longer and make a vacation out of it. But, my guess is that since you'll need to be a pioneer or elder for 15 years there won't be a lot of big money on this trip. Perhaps that's why they picked pioneering for 15 years, to ensure that the U.S. friends are more monetarily depressed and therefore not off-putting to the foreign friends? Maybe.