An insurer may invest any of its funds, in an aggregate amount not exceeding fifteen percent (15%) of its assets in preferred stocks or shares, other than common stocks, of solvent institutions existing under the laws of the United States or of any state, district, or territory thereof, or of the government of Canada or any province thereof, if all of the prior obligations and prior preferred stocks, if any, of such institution at the date of acquisition by the insurer are not then in default as to principal, interest or dividends.