To test the transfer of data from Simulink to the Arduino, and back, just use Serial. Write what you read.
When you have some idea how long that takes, you can use Serial1 for whatever else it is you need to do. What that is is not at all clear.
r = char(r)' %converting back to binary
That comment is nonsense. The binary data in the memory location designated by the typeless variable r does NOT need converting to binary data. Depending on whether char is signed or unsigned, using char() may actually be causing more harm than good.