I got this done on my fourth attempt I can't believe I did it
Splits:
World 1: 2;08.700
World 2: 2;51.080
World 3: 2;55.520
World 4: 2;41.200
World 5: 4;01.293
Videos I used as guides I found helpful for routing:
Chairity Diary: • Marathon in Under 15 Minutes Achievement —... (has some slightly slower but much more consistent routes)
QETC: • Verlet Swing Marathon Speedrun - 14:57.123 (gives a good idea of what time to be at when at the start of each world, good routing, big confidence boost for me)
BertyBob: • [Former WR] Verlet Swing Speedrun | Marath... (the WR run, has some fast strats that were helpful too, he even pinned my comment!)
Just practice every level until you can get them all consistently. Especially world 5. Level 100 make sure to do the hot dog swing, it's way more consistent and the buoy cycle is better.