Low speed through diskstation?

Hi,

using vyprvpn through Synology diskstation I only get a download speed of max. 3.5 MBit/sec.
(deactiving vpn a lot of faster). It’s configured as openVpn connection.
Is anybody facing the same issue? Any tipps?
I already tried several servers, but always the same.
Of course using the vpn does slow down, but only 3.5 MBit/sec really is very slow.

Regards