I have a bunch of files that are usually updated with power query from other excel files in .xlsx format. But recently they'd become too big (about 250Mb), so I decided to switch them to .xlsb. However, all querys have become extreamly slow: refreshment time have increased form ~5 min to 30+ min. The Internet connection remains the same, so it's unlikely that the slow-down is due to Internet speed.
I didn't manage to find any relevant info in google, maybe here anybudy knows if it is possible to make .xlsb files load more quickly.