The announcement came as the civil society collective Aar Sunu Election (Protect Our Election) said it had organised a new rally for Saturday.
The collective is calling for an election to be held before April 2, when Sall's term officially runs out.
It says the vote — originally scheduled for February 25— must be held by March 3 at the latest.
"An inexplicable slowness has been noted. Nothing has been done" despite developments over the past week, the 15 candidates said in a joint statement released late on Tuesday.
"Everything is moving at the pace of President Macky Sall's ill will," the statement added.
Sall's last-minute delay to the February vote plunged the traditionally stable West African nation into its worst political crisis in decades and sparked unrest during which three people were killed.
The opposition denounced the move as a "constitutional coup."
Last week, Senegal's Constitutional Council overturned the vote delay and called on the president to organise the poll "as soon as possible."
However, it left open the question of when the election will be organized.
"Everything suggests that Macky Sall cannot come to terms with the fact that his attempt to sabotage the presidential election was thwarted by the Constitutional Council and the people," the 15 candidates said.
They announced "a series of actions aimed at ensuring that the election is held within the allotted time."
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