Use and Meaning of Capacity: Capacity Dropped below 15 %

Solution 1:

I imagine that you have seen dictionary definitions supporting your interpretation of capacity as the maximum that can be held.

For example,

Capacity = the total amount that can be contained or produced

Cambridge dictionary

The use of the word in your sentence is a shortened form of “residual capacity”, the amount of the maximum that remains to hold new admissions to ICUs. If 85% of the (maximum) capacity is already in use, the residual is 15%. Hence we may understand that in some regions the amount of (maximum) capacity already in use rose above 85%, thus reducing (residual) capacity to less than 15%.

Or it may be similarly interpreted to mean the capacity available to accept new admissions to the ICU. As patient numbers in the unit increase, the available capacity decreases.