We normally recommend 50Mbps or more, and low latency to other NKN nodes. It will definitely speed up your initial sync, as well as improve your mining yields. The better your Internet connection, more of your NKN Neighbor nodes will select you for next hop, and you relay more data, and in turn (statistically speaking) earn more mining reward.
Purely from the amount of data exchanges between nodes on a quiet day, 8Mbps might be sufficient. But you probably have to run some long-term A/B test to decide the effects. I believe in our Discord mining channel, ScottAC and JustChill have lots of experience setting up larger mining operations with own VMs on barebone machines. You can ask them too.