Yes, Primeape is very beatable.
For these calculations, both Pokémon are level 50, and Primeape has 25 SpD IVs, like you said.
252+ SpA Chandelure Flamethrower vs. 0 HP / 0 SpD Primeape: 127-150 (90.7 - 107.1%) -- 43.8% chance to OHKO
252+ SpA Chandelure Overheat vs. 0 HP / 0 SpD Primeape: 183-216 (130.7 - 154.2%) -- guaranteed OHKO
While both Flamethrower and Overheat can OHKO, Overheat is a guaranteed KO. However, if you opt for Flamethrower, you won't have to switch out after KOing Primeape. Let's see how Chandelure does against Night Slash:
Jolly
252 Atk Primeape Night Slash vs. 0 HP / 0 Def Chandelure: 76-90 (56.2 - 66.6%) -- guaranteed 2HKO
252 Atk Primeape Night Slash vs. 0 HP / 0 Def Chandelure on a critical hit: 112-134 (82.9 - 99.2%) -- guaranteed 2HKO
Adamant
252+ Atk Primeape Night Slash vs. 0 HP / 0 Def Chandelure: 84-100 (62.2 - 74%) -- guaranteed 2HKO
252+ Atk Primeape Night Slash vs. 0 HP / 0 Def Chandelure on a critical hit: 126-150 (93.3 - 111.1%) -- 62.5% chance to OHKO
While this is assuming no Choice Band, Expert Belt or Life Orb, Chandelure can actually survive 3/4 scenarios and even has a chance of surviving the fourth. Bear in mind that these calculations assumed that Chandelure had 31IVs in Defence and HP and that Primeape has no boosting item (with a boosting item Primeape will OHKO). Finally, let's compare Speed.
Primeape: 252 Speed EVs, Jolly nature
161
Chandelure: 252 Speed EVs, Modest nature
132
Chandelure: same as above, but with the 1.5x Choice Scarf boost
198
With the Choice Scarf, you will have no problem outspeeding Primeape. Your only worry is if Overheat misses.
But wait, there's more!
To outspeed Primeape, all you need is a speed stat of 162. Factoring in the Choice Scarf, you only need 108 Speed EVs to reach 162. This leaves you with 196 EVs to put into HP or Defence, if you want to survive Night Slash in case things go wrong. But I'll leave that to you. Good luck in your battle!
