What you say you want to do is 100% do-able. Latency is not an issue.

However

That doesn't mean that you can do it - it is possible (but unlikely) that some of the components are crippled (most probably the satellite connection may be filtered).

It's also possible that this isn't a true satellite modem. One approach to satellite is a true bi-directional ground-space connection - the other is to have a 'slow' ground to ground connection for data flowing from you to the internet (ie page GETs) and then a clever bit of s/w on the PC that looks for HTTP responses on the asynchronous satellite connection (ever seen web connections served by DVB-S satellites?).

Assuming it's a bidirectional connection. the most obvious first:
you need to look at your PC firewall to ensure the vpn client can penetrate it.
You need to make sure your VPN is trying to connect via ethernet.
Can you ping your VPN (far) endpoint?