* Current account surplus rises to $65.8 bln in 2015

* Net capital outflow falls to $56.9 bln from $153 bln in 2014

* Weaker rouble mitigates impact of lower oil prices (Adds details, context and comment)

MOSCOW, Jan 18 (Reuters) - Russia’s current account surplus improved in 2015 while net capital outflows fell by almost two-thirds, underscoring the role of a weaker rouble in mitigating the impact of a slide in oil prices.

Preliminary balance of payments data published by the central bank on Monday showed the current account surplus increasing to $65.8 billion in 2015 from $58.4 billion in 2014.

Net private sector capital outflows fell to $56.9 billion in 2015 from $153 billion in 2014.

In the fourth quarter, the current account surplus was $13 billion, compared with $7.5 billion in the third quarter. Net capital outflows reached $9.2 billion compared with a $3.4 billion inflow in the previous quarter.

“The current account looks strong,” said Dmitry Polevoy, chief Russia economist at ING Bank. “We are still seeing the effects which the market expected on the back of the rouble decline and economic recession.”

Although lower oil prices led to a sharp fall in export revenues last year, this has in part been offset by lower imports, as the weaker rouble and lower incomes led Russians to curtail spending on foreign goods.

The improving balance of payments represents a stark contrast with the situation in 2014, when central bank reserves shrank by $107.5 billion as Russia grappled both with plunging export revenues and a surge in capital flight.

In 2015, the reserves rose by $1.3 billion, indicating net investment outflows were broadly matched by net earnings from trade and foreign investments.

In an accompanying statement, the central bank said the current account improvement reflected a smaller deficit for services and investment income, including lower debt repayments because of a decline in the national debt burden.

It also said most of the capital outflow reflected private external debt repayments - a contrast with the previous year when the outflows also reflected sizeable direct investments abroad and purchases of foreign currency by the population.

The central bank also said the most significant part of the reduction in capital outflows resulted from banks reducing their external liabilities, with other sectors also being forced to redeem foreign liabilities while being practically unable to build up foreign assets.

“Over this year we have seen the constant moderation of so-called ‘grey’ export flight, the illegal withdrawal of money. Probably this was one of the factors which helped,” said ING’s Polevoy.

“Debt payments were more manageable by the private sector and we had no excessive demand from households and corporates (for foreign currency). All this helped the capital flows too.” (Reporting by Jason Bush and Alexander Winning; Editing by Toby Chopra)