Verify the security, encryption of VPN

We build the network as below

The VPN server was built on CentOS and two PCs use windows 7. All three were built on VMWares. We want to check the encryption of the data so we use Wireshark to capture the packets on the IP range 172.16.1.0/24. We open a text file in local computer. Then use Wireshark on the real computer to capture the packet with the command "frame contains ..." And we see the content of the packet. Is it right or not we see the packet content? We thought if the VPN is secure, we would not see the content of the packet. Someone could give me the answer, we appreciate that so much.