3G as a hotspot is OK for browsing non-graphic intensive websites, email, and internet forums. There is a reason why it is only $15 a month. 3G can work well on a mobile device as mobile browsers are designed to work with limited bandwidth - but once you connect a laptop to the hotspot with a desktop browser you are going to see a major slow down.
Once you start looking at 4G or 4G LTE hotspots you are going to see the fine print that once you exceed a set number of Gb usage in a month the speed will be dropped to 3G, Edge, or 2G- even when the system says "unlimited".