Republican presidential candidate Marco Rubio speaks at Wellman's Pub & Rooftop in West Des Moines, Iowa, last week. (Andrew Harnik/Associated Press)

Sen. Marco Rubio's presidential campaign substantially stepped up its fundraising at the end of 2015, bringing in $14.2 million from October through December, more than double what the Republican collected the previous quarter.

But the senator from Florida still lagged behind fundraising leaders Ted Cruz, a senator from Texas, who raised $20.5 million, and retired neurosurgeon Ben Carson, who scooped up $22.6 million. And Rubio's campaign burned through more than it brought it, spending an estimated $14.8 million as it tried to bolster his standing in the crowded GOP field. Politico first reported Rubio's fundraising figures.

More than $8 million went to run television ads, more than any other GOP candidate has spent on the air, the Rubio campaign said Sunday. It ended December with nearly $10.4 million in the bank.

Rubio’s campaign disclosed raising a total of $676,000 from bundlers who are lobbyists. The bulk came from Akin Gump's Geoff Verhoff, who brought in $491,045.

The campaign's fundraising haul last quarter nearly matched the amount raised by its allied super PAC in the last half of 2015. Conservative Solutions PAC brought in $14.4 million, including $2.5 million each from billionaire hedge fund managers Paul Singer and Ken Griffin.

Anu Narayanswamy contributed to this report.