I'm about 17 episodes into critical role. I really enjoy it, but binging it can get a tad bit monotonous, so I was thinking about watching them both parallel so I can get caught up on the current game and watch it live. Does the second campaign have spoilers for the first campaign?
Yes, it's probably difficult to watch Campaign 2 without being spoiled for parts of Campaign 1
Campaign 2 is set in the same world of Exandria about twenty years after the end of Campaign 1, and some things that happened in Campaign 1 do inform what the world is like in Campaign 2 - but it is also set on a different continent a long way away from the events of the first campaign, and thus far the stories of C1 and C2 have been pretty well isolated from each other. In the story there are sometimes references or callbacks to characters or events from the first campaign which you may not catch or understand if you're not familiar with the first campaign and could be considered spoilery.
The more significant issue that, out-of-character, the cast aren't afraid of occasionally referencing or discussing the events of the previous campaign while playing - and especially in the companion show Talks
MicanaMachina if you're also intending to keep up with that while watching the second campaign (which I would personally recommend). There are often jokes and references to later events of the first campaign which may spoil those events for you if you haven't seen them yet and especially about what happened at the end of the campaign, including pretty major spoilers for how that turns out for some of the characters.
However, I do know someone who is currently keeping contemporaneous with Campaign 2 and slowly working through watching Campaign 1, and it doesn't seem to have affected his enjoyment of the show negatively.
FWIW, the earlier arcs of Critical Role's first campaign are a bit more of a slog as they were still getting to grips with the whole streaming thing and settling in to the format. They get better as time goes on and you'll probably find later episodes are more watchable (in particular you're a few episodes away from a significant change which does tighten stuff up a bit).