I find this laughable. We run over twice that many in some adventures in the same time span. Again, though, we play 1e. We tend to like exploring, planning, solving puzzles, with several fast and furious combats mixed in. Anything over 10 minutes, unless it's a major fight with the boss, and folks start yawning.
Well, to be fair, first edition does not have any combat options beyond "I hit it with my sword/dagger/bohemian earspoon"
In such a game, I would also expect for a combat to be over before 10 minutes, so that we can go back to the exploring and the puzzles.
Now, in my 4th edition game, our current combats take 45-60 minutes in average, but we expect that once we become more used to the rules, we will be able to cut that time down to 30min, so we can go back to the exploring and the puzzles faster

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Some useful props to cut down 4e combat time:
1-
Gamemastery Combat Pad or a small whiteboard for the DM to quickly track initiative, hitpoints and conditions.
2- A combat mat and minis (if you don't want to buy minis, like us, use colored glass beads and/or printed counters)
3- Give each player a small amount of playdoh (a different color for each one) so that they can place a small bit of it on each creature they are marking/cursing/quarrying
4- Combat Cards. I got jokes from my players about "tapping their encounters and dailies" at first, but after the first session everyone was sold. The cards help players visualize their options and limits book flipping to a minimum.