Short answer is they throttle by about 1/3, so 100mb not 150mb.
Does suggest an issue with Pulse and/or config of Pulse on laptop.
Strange how the work IT staff blames Virgin!
That's what IT departments do.
When you connect via VPN is all Internet traffic routed via that? (A simple trace route will confirm that). If so, what bandwidth limitations do your IT department put on routing back out to the Internet? These types of connections make double use of the works Internet. Also, what bandwidth does your company have on it's Internet connection and what per connection limits do they have?