The ways to reduce file size are: lower bit rate; lower resolution; lower frame rate; more efficient codec.
I'm assuming your current file is 720 megabytes (MB) size. If so your video's bitrate is about 10 Mb per second, which is the default setting for 1080 Apple Devices. I'm also going to assume your codec is H.264, which is very efficient.
If your video resolution is 1080 and you don't want to reduce it, you could try reducing the bit rate to see where quality starts to become objectionable, Select a short representative section; encode it and upload to test. My guess is that the quality loss will be visible somewhere around 5 Mbs – but that's depending on your content. You may be able to get away with bit rates as low as 3 Mbs if the resolution is reduced to 720.
Alternatively you could forego the trial and error approach, make peace with your slow connection, plan an overnight upload and get a good night's sleep.