One important recent study 2 found that the average duration of impact from financial crises across a range of countries over the past two centuries has been around five years. Since this current episode has been more severe than most, it is not surprising that its after-effects have lasted even longer. An exacerbating factor, too, has been the international dimension.
When a financial or a banking crisis occurs in a single economy, or in a relatively small number of countries, exchange rate depreciation is often part of the market response and part of the recovery mechanism. But there is obviously much less scope for that mechanism to work when a crisis affects large parts of the global economy simultaneously.