head to head
WWE 2K15 asks more than Dead or Alive Xtreme Beach Volleyball, and the gap is reads.

Execution · Practiced Mastery
Light volleyball timing wrapped in a gift-economy vacation sim.

Execution · Competitive PvP
Reversal timing and pacing against an opponent baiting your counters.
Dead or Alive Xtreme Beach Volleyball leans Execution (Practiced Mastery); WWE 2K15 leans Execution (Competitive PvP).
WWE 2K15 leans a little harder on execution, though the gap is small.
Dead or Alive Xtreme Beach Volleyball
Volleyball rallies need timing but stay deliberately forgiving
WWE 2K15
Reversal timing windows decide most exchanges
WWE 2K15 leans clearly harder on reads.
Dead or Alive Xtreme Beach Volleyball
Versus humans adds light shot prediction
WWE 2K15
Human opponents bait reversals and vary move timing
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Dead or Alive Xtreme Beach Volleyball
Partner mood and gift systems behave semi-randomly
WWE 2K15
Chain-wrestling rock-paper-scissors minigames add randomness
WWE 2K15 leans a little harder on optimization, though the gap is small.
Dead or Alive Xtreme Beach Volleyball
Managing partner relationships and money is the deeper loop
WWE 2K15
Move sets, stamina and match pacing are learnable systems
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.