The bandwidth command sets a minimum amount of guaranteed bandwidth, when there's congestion. Assuming your physical interfaces are not running at 30 Mbps, the bandwidth command would not doing anything until the physical interface congested. However, the bandwidth command can proportion shaped bandwidth in a child policy, which is noted in my original post.
As to what "one person suggested", a policer can be used instead of a shaper. However, it discards overrate traffic while the shaper queues overrate traffic. What's suggested could be used on the uplink to the Internet as an egress policy. It could also be used as an egress policy on the interface toward the firewalls, but then you would want to set it to 15 Mbps. It could also be used as an ingress policy on those interfaces too, although if you use it as an ingress and egress policy, you wouldn't need to configure all three interfaces, you would only need to configure the Internet link or both firewall links.
Shaper and policer behavior can overlap in how they treat traffic. Normally I recommend a shaper, when it's available.
