We are a small business company that is based in Sydney and opened a new office in London.

Number of employees in Sydney office is 25 and in London is 6 employees.

So the traffic isn't that high. Files to be transferred are

Excel sheets with size of 15mb max.

Both locations have

MS server 2008 and Fortigate gateways.

I set up a site to site vpn but it's extremely slow. Maybe this is because

our upload speeds is 1Mbps only but We will 
increase the upload speed to 20 Mbps in both locations 

but I am afraid that this will not solve the problem as the 2 locations are far from each other and the upload upgrade won't solve the problem. what's the best way to go? Shall we find a provider for the VPN? or is there another technology that can be used through internet without paying extra costs? Many thanks!