Here is what I did:
1. Change the Settings
To make this easy, go to Gameplay Settings and set the Submission Mini-Game to Rapid. Then, adjust the Submission Mini-Game sliders:
Player Button Press Strength: 100
Player Wrong Press Penalty: 0
AI Button Press Strength: 0
AI Wrong Press Penalty: 100
2. Match Setup
Character: Rhea Ripley.
Opponent: Iyo Sky.
Difficulty: Legend.
Match Type: Iron Man Match, Customize Match Time Limit: 15 Minutes.
Win Condition: Change to Submission Only.
Arena: Evolution (Recommended for its large stage area).
3. During the Match
Get an Early Lead: Use your submission sliders to submit Iyo Sky immediately at the start of the match.
Build a Safety Net: I recommend getting a lead of 3 to 5 points within the first few minutes to be safe.
The Great Escape: Once you have the lead, leave the ring and run to the large stage area in the Evolution arena.
Waste the Clock: Stay on the stage and move from one end to the other to keep Iyo Sky chasing you. If she gets close, reverse her attack, knock her down, and move to the other side again.
The Win: Keep this up until the 15 minute timer hits zero. As long as you have more points than Iyo, you will win the match.
Once the match is won, the achievement will pop.