Is there any cellular phone service that throttles to a usable speed (say at least 1.5 Mbps)? I was looking forward to the spread of 4G because I naively though

Is there any cellular phone service that throttles to a usable speed (say at least 1.5 Mbps)? I was looking forward to the spread of 4G because I naively thought throttled speeds would also increase to "3G equivalent" instead of "2G equivalent". I use Mint Mobile and last month I hit the 4G data cap of my "unlimited" plan (30 Gb). I tried to buy more data, but it can't be done on the "unlimited" plan. I could not buy more data for my "unlimited" data plan after my "unlimited" data plan ran out of data. Other plans let you purchase additional data at an expensive price, only the "unlimited" plan doesn't.