Slow internet speed with screen share

When I do screen share my internet speed on my phone go down to 5 Mbps and without screenshare its ~50Mbps. I am connecting from my iphone 7. I used another iPhone to test this scenario and same result of slow speed. Is it suppose to happen? Something wrong here? Btw, My apple tv is connected with wired ethernet cable and there it shows good 90Mbps speed. All tested with speedtest app.