15-20 Mbps uplink will be enough for most situations, at 4K. It's not like you'll be streaming ProRes or some other minimal/no-compression data. You should be encoding a compressed stream and sending that to the streaming service. For 1080p, you can probably get by with 10-15 Mbps up, though it is better to have more bandwidth since you might have other things pushing data up at the same time.