If you're playing out individual battles, not campaigns, you don't need MekHQ. MegaMek will easily manage lance-on-lance battles, and if you run out of time, you can save the game to finish later.
Be aware that setting up a MegaMek battle takes a bit of time and attention, and the procedure is not clearly documented or explained. If you start the battle, then realize that you forgot to set something like the map size (it defaults to a single random mapsheet), optional rules, or starting locations, it's too late, and you've got to do the whole thing over from scratch. Once you work out a routine to do everything in some kind of order and become familiar with it, it's not that bad, but without a routine you're probably going to make mistakes....a lot.