I don't understand this either. Online play seems to slow it up even more. It seems like (at least as a player) my turn takes no time at all. Yes, I plan my attack ahead of time (which may change if the situation/layout severely changes), but I don't understand why my attack with resolution (marking the damage and such on the baddies sheet) takes about a minute, MAYBE 2, but other players will seriously eat up about 5-10 minutes on their turn. As such, 2 hours of the session are combat by other players (mine being 10 minutes total) and the DM's being about 20. 2.5 hours for 3 rounds is somewhat ridiculous (especially when you only partake in about 10 minutes of it).
Maybe if I try playing with the health/dam of baddies, it will help.