Go to your phone dialer and type *#0011#. It will take you to the screen below. Does it say LTE? You can ignore the arrow. I made it for another post. Depending on where you are, you may get the 5MHz or the 10MHz. the 10 is twice as fast.
Also, check connections > mobile networks > network mode, make sure the LTE/GSM/WCDMA option is selected.