The Short Answer
For many 15,000-gallon inground pools, start with a wall-capable mid-size cleaner and add waterline cleaning only if that surface is part of your maintenance goal. The Cayman is the simpler comparison; the current Quantum adds myDolphin Plus™ controls and top-load filtration; the Premier adds flexible filter media; and the Nautilus CC Plus Wi-Fi offers another connected-control path. Verify the exact product listing because included filters and controls can vary.
Use Gallons as a Cross-Check, Not the Size Rating
Choose by measured length, shape, and usable cable reach first. Gallons describe water volume; they do not show whether a cable can reach the far wall and deep-end floor, or how a robot will handle a long, freeform, or divided layout. A long, narrow pool can need more reach than a compact pool holding the same volume.
For a rectangular pool, gallons are approximately length × width × average depth × 7.48. Use that calculation to check the stated volume, then compare the longest dimension and cable-routing requirements with the current product manual. Steps, shelves, islands, depth changes, and the required power-supply location can all reduce practical coverage.
Use Debris to Break the Tie
For settled dust or pollen, compare the available fine-filter options; for regular leaf loads, compare intake opening, basket capacity, and how often the filter must be emptied. A larger filter delays maintenance only when the debris can enter it, and no underwater robot replaces surface skimming.
Verify Coverage in Your Pool
- Observe whether the cleaner crosses the floor-to-wall transition instead of assuming every wall-capable model will suit every shape.
- Check the far end and deep-end floor after a full cycle for repeat misses.
- Brush steps and shallow shelves toward the main floor when they remain outside the robot's route.
- Rinse the filter and inspect brushes and intake after heavy cleanup rather than waiting for reduced pickup.
Compare more pool-type considerations in the inground guide and use the budget category only after confirming fit; live product cards are a better source for current price than a fixed price promise.
