By default browser makes only 6 outgoing connections in parallel. However it can be increased through registry to make it faster.
You need not restart machine. Just restarting IE is good enough. It might not make a huge difference but atleast won’t harm and seems speeding up a little bit specially if you are accessing webpages from remote site locations with internet latency.
In addition to this, there is another article which I posted previously which shows how to speed up rendering of forms in Internet Explorer if you are loading data by making API calls to a different domain from where form is being rendered.