Too much traffic with gre protocol

Hello,

I just realliced that I have too much traffic through the only WAN interface on this site, this is a very slow connection, about 5 Mbps simetric.
When I opened “ip → firewall → connections” and I sorted by “Orig/Repl. Rate”, I realliced that the connection with the most traffic is the gre VPN itself.
The VPN is GRE and the only settings about IPsec is the secret writted in the GRE interface itself, nothing was configured in “/ip ipsec”
I hope the following image can be showed (if not, please tell me where can I upload it):

The same traffic is also been showed in the other site of the VPN, and I can see it in “/tools graphing” in the other direction (Tx in one site and Rx in the other site)
What could be the problem?
If I ping somewhere in the other site, using private IP, I can see the connection as a separate item, with protocop icmp, not gre. So it seems that the tunnel itself is taking too much bandwidth

Any idea?
Thanks in advance.
Regards
Damián

Any idea?