When using a VPN service, all the traffic that is usually* sent directly from and to remote hosts is now tunnelled over one other host: the remote VPN gateway.
Of course, this will be your bottleneck. Once connected to a VPN gateway, your complete throughput will be determined by the up- and download speed of the gateway and its capabilities of handling the traffic—remember that you might be sharing your VPN connection with several other users, and they all might use the same gateway.
You theoretically "keep" your original 160 Mbit/s speed, but if you decide to send all traffic over the slow link, then you can't really make much use of it.
* I say "usually" because there are VPN configurations where not all traffic is sent through the tunnel, but only selected IP ranges will go through the VPN gateway. A company mail server might require you to be connected to their VPN gateway in order to be able to route to it. This will not affect all your other Internet traffic though.