Twenty five years isn't. As Bashir says in "Way of the Warrior,"The seventy years between Khitomer and the beginning of TNG is a long time.
"Two decades of peace with the Klingons and it all comes down to this."
Two decades puts the date almost exactly 50 years after Praxis, which is pretty much exactly when Spock predicted their supply of oxygen was going to run out. Which means they didn't get help from the Federation BEFORE then, which basically means the only reason the Klingons still exist as an "empire" and not a gaggle of planetless nomads is because the Federation saved their asses.
It's extremely unlikely they still went on with their conquests after TUC, since that would pretty much negate the ENTIRE PREMISE of that movie. If the Klingons were still capable of that, Gorkon's peace overtures would be completely absurd; there'd be no REASON to talk peace with the Federation since the Empire is still dong just fine and can go and conquer all it likes.
OTOH, right around the time Qonos was running out of oxygen we had the Romulans started attacking Klingon colonies (most notably Narendra III and Khitomer) and an inconclusive eighteen year long war with the Cardassians. It's no coincidence that the Klingons became friends with the Federation right AFTER that and gave up conquest as a way of life until "War of the Warrior."