Lower for longer, then what?

I do not think that Yellen's promise of "lower for longer" is profitable and will push up the US economic growth. Recently we can see an increase in default rates, and lower interest rates allow companies, especially those big companies, to increase their gearing ratios. Therefore, the risk of the banking sector increases. Moreover, when loans become cheaper, some successful and large private companies may decide to stay private. In the first three months of 2016, only 9 US companies succeeded in listing, but 21 were forced to shelve IPOs. The major challenge of the US economy is exogenous. Therefore, the promise of "lower for longer" is only profitable when there is no breakout of exogenous crisis.