Qsync : Too slow to synchronize

[Mt. take]

Qsync synchronize very very slowly.

I use TS-131.
TS-131 is connect to internet.

There are 4 PC(two windows 8.1 pro 64bit and 2 windows7 pro 64 bit) .
PC is connect to TS-131 by internet.
I made one qsync folder.
All PC use same administrator account and they use same qsync folder.

It is too late to synchronize.

For example, I made 150KB PDF file and I update 300KB excel file.
But for finishing synchronize, It takes about 1 hour.

Connection traffic speed is 8mbps or up, still there is a margin in line speed.
But traffic speed does not increase.

CPU load was high, so I got off to a version control.
CPU usage dropped from 50% to 25%.

BUT still synchro is too slow.

Would this be specifications?
Something should I do?
My use of Qsync is wrong?

I'm looking forward to your advice.

Best Regards.