Floor 14 and 15 have very frustrating Randoms that manage kill off my team...
And I can't beat the bosses on those floors due to said Randoms... Anyone have advice?
After the triple boss, all the floors tend to have pretty nasty trash. Just enjoy the challenge and push on. Trash, unlike bosses, tend to become easy after a little bit of grinding really fast. I mean you don't have to grind just to handle the trash, but explore the map, lose some dudes, go back to town, level up, etc, etc. By the time you're done the floor they tend to be less bad. Some tend to stay pretty ridiculous though, helbelmares come to mind.
For floors 14 and 15 specifically. I'm willing to rekon that you're having grief with bronze golems and black enmels. Neither really require a strategy other than OMGOMGNUKE IT NUKE IT NOW pretty much. Neither have any elemental weaknesses either, and both are immune to paralize. Joy.
Marisa's astroid belt should do decently against the black enmels (yes, astroid belt, it pierces high mnd targets better than her other spells excluding master spark), you might also have luck with Patchy's silent selene, Princess undine wont be any better for them, so don't use it. Rumia's dark side of the moon will work WONDERS, use that if you use her. I remember on my first playthru I just had to run away because everyone that I was using couldn't do better than 0.
Bronze golems are simpler, they don't have crazy defense, just high hp. So focus fire on them and paralize the other enemies if need be. They are not immune to debuffs, so you can also try that if you really have no chance.
Enjoy the next floor though, helbelmares are like blackenmels with 5X more hp, and cast the same spells, only MUCH stronger.
I seem to recall the trash after floor 16 stays relatively difficult compared to most JRPGS, but wont have any super nasty enemies in particular.