Switzerland's Toni Rominger was up with the leaders at the end of the 226km stage from Santo Domingo de Calozada to Santander and retained the race leader's yellow jersey he took from his compatriot Alex Zulle on Sunday.
Lauritzen made his break with the Italian Bruno Leali after 135km. The pair took advantage of appalling visibility at high altitude to establish an advantage of more than three minutes. But Lauritzen's lead was down to 20 seconds five kilometres from the finish.
However, lurching from side to side, Lauritzen held off the desperate final sprint of Laurent Jalabert, of France.
Today's 16th stage over 173km from Santander to Alto Campoo is another mountain trial. It including two first category climbs before a 12.5km special category haul to the finish at 1,625 metres.Reuse content