[edit] never mind, you're right, assuming an 8N1 configuration - 8 bit bytes, 1 start bit, 1 stop bit, and no parity bits.
So 3kB/s, if your site is 15kB you're looking at 5 seconds per request, or 0.2 rps.
Plus overhead. I thought my original math sounded too fast.
[0] https://www.linuxjournal.com/files/linuxjournal.com/linuxjou...
[edit] never mind, you're right, assuming an 8N1 configuration - 8 bit bytes, 1 start bit, 1 stop bit, and no parity bits.