After more than a million migrants poured across the Mediterranean a year ago, European nations tightened border controls and set up naval patrols to stop smugglers.
Sigmar Gabriel, Germany's vice chancellor, said the influx was still a record number and that Merkel had "underestimated" the challenge of integrating new arrivals and finding them jobs.
Weise told the weekly Bild am Sonntag the new figure for 2015, which excludes duplicate registrations and people who traveled on to other countries, is lower than one million.
A series of attacks in Germany on civilians last month, including two claimed by terror group the Islamic State (Isis), have led to calls from opposition politicians and some citizens for Merkel to halt her government's policy that has seen hundreds of thousands of refugees enter the country.
Support for Merkel has fallen precipitously over the past year as the public has become enraged by Merekel's open-door migrant policy that saw Germany accept 2.14 million refugees in 2015 alone according to the Federal Statistics Office. On Friday in Warsaw, she appeared alongside leaders from the Visegrad Four countries - Slovakia, the Czech Republic, Poland and Hungary - which have criticized her open-door policy for refugees. A nationalist party to the right of Merkel's Christian Democrats has received a surge in support and chancellor, who has stuck by her motto "we will manage", has seen her popularity ratings fall.
In her interview Sunday, Merkel declined to say whether she would run again.
A recent poll by Emnid revealed that 50 percent of German nationals oppose Merkel's potential run for the fourth chancellor's term, while 42 percent of Germans support Merkel's appointment as the next chancellor.