Always ask questions:
MERV 15 is such a fine mesh rate it will cause a normal residential HVAC system to run very inefficiently due to the constricted airflow over the evaporator and possibly over amp the fan motor in the air handler. I wouldn’t recommend anything higher than a MERV 11 for that reason. You are 100% right about metering outside air in based on CO2 counts, that’s how a lot of modern HVAC equipment is design for controlling outside air economizers. A lot of older commercial airbags sling equipment is also not designed to accommodate any any outside air changes.
Don’t forget UV lighting in the air handling unit. That is a lot more effective than even HEPA rated MERV 17 filters used in hospitals. UV lighting, maximum air changes per hour and maximum outside air intake is what the CDC in conjunction with ASHREA is recommending fir controlling infectious aerosols.