Rclone sync behavior

If i have a, say 15GB file and the next time i run sync that file is modified, will rclone only upload the changed portions or will it upload the whole file and overwrite the old one on the destination?

I don’t know specifically but I would assume [edit for clarification: full file upload] so (at least for most of the remotes). I think usually there’s no capability like for rsync to have partial block checksums computed remotely (so you’d have to actually download the whole file to see what changed, not entirely productive) plus I don’t think most remotes allow for random writes inside existing files.