If each calculation is independent (as in, you don't need the entire 15000000x1 cell to make 1 calculation), then you could rewrite the parfor loop to work on a sliced variable. Workers will only receive a "slice" of the large 15000000x1 cell. This prevents passing the large cell as a broadcast variable, which will use too much memory.
The parfor loop should look something like this:
LargeCell = repmat({zeros(24)}, 100, 1); %Represent your 15000000x1 cell
Results = zeros(size(LargeCell)); %Store results here
parfor k = 1:length(LargeCell)
Results(k) = complex_function( LargeCell{k} ); %Do your CPU-intensive calculation here
end
