One of my two campaigns on Roll20 just finished Episode 1 of Hoard of the Dragon Queen tonight. We ended up running all the missions. Although I realize that the module doesn’t actually require that, various circumstances with player availability meant that it ended up being easiest way to handle things on a session-to-session basis. That yields a lot of experience, by the way, even when I scaled down some encounters due to having three characters instead of four in some encounters. If they get enough random encounters in the village and complete all the missions (including bonus objectives), then hitting level 3 while still in Greenest can happen. That may change some calculations down the line, but I expect I will deal with that as it happens.
Hoard of the Dragon Queen isn’t really for GMs or groups completely new to RPGs or even D&D, though. People in that situation should try out the Starter Set (which has a more cohesive narrative and, for me, is lots more fun). I’m glad I had several sessions of Fifth Edition under my belt as both a player and GM before starting this. Also, if you run this online (or maybe even offline), give a thought to buying the Hoard of the Dragon Queen maps. They don’t cost much and artists deserve to be paid.
WARNING: The rest of this post contains spoilers for the module.