A simple "Simple Queue" should do the trick.
On each end of your tunnel, add a simple queue with the local subnet as target and the remote subnet as as "dst" and fill both "Max Limit" fields with your desired total b/w. like "60M".
After reading your post again, I get you want to limit file sharing only, correct? Either you put your fileserver in "dst" or you'll need to go the mangle way and mark packets for file sharing, you could match by protocol/port to filter file sharing protocols or dst-addresses for file servers in general.
Leave the rest untouched.
That should be it.
OK, I just did a test, I made a 1mb queue for the server ip in the matrix and made a copy of a branch file, was 1mb right, the file server for now will be another server with another IP so let's say that would already be right correct? But could we just join these two servers and I would have to mangle it? But I didn't think how to do it, I worked very little with him.
Sorry English, I'm using google translator.