Simulink real time I/0 mode

Hi I'm using simulink in SDRT I/0 mode to visualize and analyze my signal.

I use the packet input and a matlab function to parse the data

and this is the function

function [ch1, ch2, valid] = parsePacketBuffered(pkt, ready)
%#codegen
persistent buf
if isempty(buf)
    buf = zeros(1, 100, 'uint8');
end
ch1 = int32(0);
ch2 = int32(0);
valid = false;
if ~ready
    return;
end
m = length(pkt);
if m >= length(buf)
    buf(:) = pkt(end-length(buf)+1:end);
else
    buf(1:end-m) = buf(m+1:end);
    buf(end-m+1:end) = pkt;
end
% cerca l'ULTIMO frame valido, non il primo
for i = (length(buf)-9):-1:1
    if buf(i) == uint8(123) && buf(i+9) == uint8(125)
        raw1 = uint32(buf(i+1)) + ...
            bitshift(uint32(buf(i+2)), 8) + ...
            bitshift(uint32(buf(i+3)), 16) + ...
            bitshift(uint32(buf(i+4)), 24);
        raw2 = uint32(buf(i+5)) + ...
            bitshift(uint32(buf(i+6)), 8) + ...
            bitshift(uint32(buf(i+7)), 16) + ...
            bitshift(uint32(buf(i+8)), 24);
        ch1 = typecast(raw1, 'int32');
        ch2 = typecast(raw2, 'int32');
        valid = true;
        return;
    end
end

PROBLEM IS: there is a 1.5s latency between the plot in simulink and the same plot done in phyton. What can be the issue? What am I missing?