While 401(k) accounts have benefited from double-digit returns over the past few years, plan participants might not want to budget big for retirement quite yet, according to Russell Investments' 2015 Annual Global Outlook.

Key market predictions and economic forecasts for the coming year paint a slower, less volatile picture, with gains in the single digits, Fed tightening around the middle of the year, gradual improvement in the unemployment situation and a bump in 10-year Treasury yields.

In addition, other countries' central banks pursuing differing strategies will offer varying risks and opportunities. While strategists expect the situation will "turn out smoothly," they added in the report that "markets could be spooked if inflation pressures emerge and force more aggressive Fed action, or if Europe and Japan fail to respond to more stimulus."