STOCKHOLM (Reuters) – Soaring interest rates and too much debt are weighing down Sweden’ commercial real estate firms, making them the biggest threat to financial stability. The full effect of recent rate hikes has yet to be felt and authorities have told Sweden’s banks to hold on to capital in case the situation deteriorates and loans turn sour. Worries about the sector have affected the crown currency and foreign investors have reduced holdings in Swedish assets. After a banking crash in the 1990s in Sweden – also caused by the commercial real estate sector – the economy shrank three years i…