If you're using an emulator, you can just grind by using the speed button.
That's what I did. As soon as you get to the club... go west to the chimera lab. There is a Ostrelephant there that gives hundreds of exp a pop with a hot spring in the next frame to the left. Got from lvl 21 to 28 at a pretty nice speed (since it takes 3-4 PK loves to drop him).
Another spot for this is inside the Lightning Tower. There is a room with 5 weak monsters (moles with brain cases or something) and you can enter/ exit the room and wipe the floor with them many times before you use up all of your PP healing yourself... and a few frames over is one of those healing capsuls. Do this a few times and the rest of the game becomes much, much easier.
The last spot for this is outside of
Saturn Valley. Keep popping the roaches and the shrooms until you run out of PP for healing... then go back in to the hotspring, restore your pp/hp, and go back out again. I only did it this time so I could farm enough DP to stash several Cup of Life Noodles... but it was mad exp anyways.
It's only worth doing this when you have a character with heal though... since healing items/ DP can be hard to come by, but yeah... being over leveled made the game a hell of a lot easier without taking too much time.
Also... I haven't had any problems doing combos since I learned how to do them. I use a standard issue VBA emulator with these settings. Vsync, Render Method: Direct3D, 0 frameskip, and automatic frameskip disabled. There are certain areas in the game that have slowdowns for a few seconds (4-6 areas, it wasn't a whole lot), but for the most part I run at 100% speed with no visible lag.