22mb with 2 bars is good. You might get increased speeds with an antenna. I get 70mbps with the built in antenna with 5 bars with the same hardware you have (b311) It all depends though. Do you live in a high populated area? Is there a high populated area within a few miles of you?
Though, there is no harm in buying an external antenna. Most of these items can be sent back with a 30 day money back guarantee. If there is no increase of speed then send it back.
This helped me find the mast my b311 uses. Type in your post code, head to the b311 router page, sign in, click advanced tab, system, device information then note down "cell_id" number. Look for Threes masts close by on the map and try find the cell your device uses. This has useful information that could help determine what speeds you are capable of at your current location. This can't rule out cell congestion unfortunately. It will help determine distance from mast and will give you a good idea, as you know the area, if anything is obstructing line of site.
P.S I don't know how accurate cellmapper is. Locations of masts could be wrong. All i know is it had my correct cell id and that the info it gave me correlates with the speeds i'm getting.
Edited by woodmass14 (Tue 19-Mar-19 00:49:38)