Different Upload time of same files in Client and Web Interface

I tried uploading 250 MB of files (all the same size - 5 MB) on my seafile server and compare the required time. I am just surprised about the result.
I’m using a raspberry pi 2 model b as my server and for 50x5MB it needed 1 minute and 2 seconds to upload the files on the webinterface.
But on the client it just needed 9 seconds!

I repeated it several times and still get the same result. The files also are visible on the webinterface so the upload worked as well.

Has anyone an explanation for me why the difference is that high?