Because the file system is not as optimized as the desktop software as of R2019a, calls to function which save or write files on the file system slow down the execution time.
So, if you see such a slow down and you see a high difference between the desktop release and MATLAB Online, please check for commands which write or save data and comment them out.
Our development team will improve the performance in the future.
If this is not the cause, please create a Technical Support case:
