You can get a 4G home gateway or CPE, and fix an outdoor antenna to outside your house.

If you plan to do the traditional port forwarding and expose cctv stream to internet, you're most likely out of luck because Digi LTE is NAT-ed. In other word, you are not able to expose your web services to external web, unless you're using third party relay server to do so.

The download depends on various factors including the server's uplink capability. If the host you are downloading from is not performing well, your download speed will be still be slow regardless of which telco you are using.

Of course sometimes it also depends on the telco's bandwidth to the host too. If a lot of people from the same telco are downloading files or using the service from the same host, most likely the 'pipe' of the telco is not big enough to cater for the bandwidth demand of its users.

And speedtest is just giving you a reference of your telco's connection, and it is not necesssary to translate the same performance too all internet services you are using.