No single risk shall be assumed by a mutual assessment life, accident and sickness insurer if the risk exceeds fifteen percent of the company’s total surplus to policyowners. Any risk or portion of any risk that has been reinsured in accordance with § 38.2-3922 shall be deducted in determining the limitation of risk prescribed by this section. For the purposes of this section the amount of surplus to policyowners shall be determined on the basis of the last sworn statement of the insurer, or the last report of examination filed with the Commission, whichever is more recent at the time the risk is assumed. Mutual assessment life, accident and sickness insurers licensed on July 1, 1985, shall conform to this limitation by July 1, 1990. Until July 1, 1986, the single risk limit, after deducting for reinsurance, shall be twenty-five percent of surplus to policyowners. Between July 1, 1986, and July 1, 1988, single risk limits, after deducting for reinsurance, shall be twenty percent of surplus to policyowners. This section shall not apply to insurance coverages defined in §§ 38.2-108 and 38.2-109 and Medicare supplement insurance defined in § 38.2-3600.