You didn't say which plan you are on but I am going to guess the base plan. You would be experiencing deprioritized data, speeds will slow down when there is a lot or Verizon post paid traffic on your towers. Visible base plan customers get whatever bandwidth is available. I am on the base plan in a 4G LTE only area and I get around 15 to 35Mbps, I will have times during the daytime where it will even be less than 1Mbps. My up speeds are maybe 2Mbps at most. Another reason I don't get such great speeds is I am quite far from towers in my rural area so I only have 1-2 bars. If I am close to the towers I can hit over 50Mbps or more down, actually one trip to town I hit over 150Mbps, up speeds are >20Mbps.
If you are looking for faster speeds while on mobile data is upgrade to the Plus plan and you will get 50GB of premium data, same as if you were a Verizon post paid customer does. 4G and 5G data counts towards this 50GB allotment, 5GUW doesn't. When you use it up the allotment you will again be de-prioritized.
