The Safe Travels for Visitors to the USA is a fixed dollar based limited plan. For Limited plans, the policy maximums are just the outer limit, but for every service or treatment, the plan pays a limited fixed amount. You are right, for people above 70, the plan covers up to a maximum of $15,000 for an acute onset of a pre-existing condition. Just as the policy maximum is the outer maximum, for the acute onset of the pre-existing condition too, the $15,000 is just the outer limit. For every service or treatment, in case of acute onset of pre-existing conditions, the internal limits would apply.
Insurance rates are regulated by law. You can't find the same insurance plan for a lower price anywhere else