anon_max_rate=200 limits your users to 200 bytes per second.
anon_max_rate=0 means there is no limit !
But if the users are not anonymous this will have no effect on them.
It is not clear where the ftp server is, and where the clients are in relation to it.
If the clients are outside the LAN where the ftp server is, then they will only get files at your internet connections UPLOAD speed, which is probably not 150KB/sec.
If the clients are inside the LAN and the ftp server is on the internet, then the problem may be outside your control.
Only if client and server are both inside the LAN can you expect fast speeds. But it depends on the file size too. You need to test it using a large file, at least 50 MB to see the true speed capability. A 100K text file won't ever achieve 150KB/sec because of session overheads.