I can only guess the connectivity between your mast and the Internet is awfully congested, and/or you are in the middle of nowhere.
One of the reasons starlink does as well as it does is the ground stations are well connected to the wider world, whereas your nearest cell mast might not be.
over a mobile network? My best rtt to azure or aws over tmobile or verizon is 113ms vs 13ms over my fiber conection.