Those speeds are terrible for Verizon LTE, especially in a major metro area.
Have you contacted VZW support? They are very responsive, especially through twitter @vzwsupport
It could be the tower is saturated, but I would imagine a mad house like Vegas is engineered with a lot of capacity.
If you are eligible, trade up to a newer jetpack with xLTE support. On an updated tower in a big city, I see 50-60mbit up and down over xLTE on my Moto Pure.
I've actually stopped using my Sleek, in most cases my Moto performs better without, and I'm not sure my older 4g Sleek supports the new xLTE band.