Is you bandwidth up&down 150MBps? The transfer speed might differ greatly depending on the contract you have with your ISP. Please check if your contract says you will get a minimum or maximum of 150MBps download speed. On top of that, are you sure you're using the right units? Most bandwidth contracts have Megabits specified instead of Megabytes - it is highly important which unit are we speaking about as 1 Megabit equals only 0.125 of a Megabyte.
On top of that, there are multiple factors which can determine your real top download speed including your network equipment (routers, switches, cables, NICs etc.) and network configuration in the environment in general. I'd say the speed of 80 Megabytes is pretty good and if you don't have an enterprise grade contract with the ISP, I wouldn't expect much better performance.
There are few thing you should take into consideration:
- what's the latency on the bandwidth? If you have a high bandwidth & latency link, then it might be considered a long-fat-network or LFN by the system (http://en.wikipedia.org/wiki/Long_fat_network)
- vSphere tries to optimize bandwidth utilization multiple VMs replicating all at once. It is similar to how one huge CPU task will be finished slower on a 2GHz dual core processor than a single core 3GHz; while at the same time, two smaller tasks would be completed faster on dual core.
- it is possible to tweak some advanced config options to increase the number of transfer buffers available for disks. Check out this blog for details: http://blogs.vmware.com/vsphere/2012/06/increasing-vr-bandwidth.html