LB2120 slow streaming

i'm using a lb2120 with a t-mobile sim into a video decoder to download a live stream of our church service from our broadcast location, and streaming live at our remote location. i'm using the lan port - i have tried using 2 of them into a multi wan router, and just individually connected to our decoder. i can speed test just fine, and average around 15mbps up/down, however when i do a bandwidht test in my decoder, it's downloading video at 1.4mbps, which will not allow me to playback a video anywhere within 20 minutes of real time. 

i've spent hours on the phone with our live stream hardware provider and t-mobile, they are assuring me it's nothing on their end. i have plenty of data, great signal, i'm not being throttled, they don't adjust bandwidth for any reason even concerning video downloading, and it's not the decoder because i can plug into my home internet and it's 50mbps download. on my decoder im showing consistent latency of up to 1000 milliseconds, prohibiting me from getting all the packets i need on time. 

im wondering if anyone has had latency issues with this modem regarding streaming or downloading video/content.