HELP! file transfers take forever

We’re having a intermittent problem with openfire.

we are about 20 computers using spark 2.5.8 Mac and openfire 3.6.4

pretty much all computers run os x 10.5.8

when some users send a couple MB file, lets say 5 mb

it takes forever on some computers to receive download it and it takes a fraction of a second on others.

i dont really understand why this would happen but i figured that increasing the file transfer cache would help.

anyone know how to accomplish this or anyone have had a similar problem and solved it somehow.

thanks