They should have kept the $15 plan as well.
Most people hardly exceed 100-200MB/month.
So for them, if only the new plan is available, it actually doubles the price. They will be paying for those who more fully use the unlimited plan.
I am all for unlimited plans, but people should realize that US tariffs are silently increasing in this booming market, while, e.g., in Europe, they are rather declining. In Spain you can get 1-2GB for 10/mo on a prepaid card (Yoigo),...