The 15 will be subject to the same visa ban and asset freezes imposed on more than 50 others as Moscow shows no sign of reversing course in Ukraine, the sources said.
The new names will be listed in the EU's official journal, likely tomorrow.
The decision was taken at a meeting of the 28 member states' ambassadors to the EU, who gathered to discuss the next step in responding to the Ukraine crisis.
The measures fall short of the full-scale economic sanctions proposed by Washington, which announced separately today that it was taking action against another seven Russian officials and 17 firms linked to President Vladimir Putin's inner circle.
With far more extensive economic ties between many member states and Moscow, the EU has balked at moving to tougher 'Phase 3' sanctions that would target Russia's economy as a whole, although leaders have agreed to begin preparation of sanctions.
"If there is additional escalation then there is the possibility to pass to Phase 3. Currently, there is no de-escalation so we think additional (Phase 2 measures) are appropriate," the European Commission said earlier today.