Different price classes - Arcam A15+ costs roughly 1.9x what Rotel A12 does. Expect it to lead on paper; the question is whether you will hear the difference through the speakers you own.
| Area | Better | Why |
|---|
| Power | A | Arcam A15+ has more power - 80W against 60W into 8 ohms. That is about 1.2dB, which is a small step in loudness but real headroom on peaks. |
| Room size | depends | We rate Arcam A15+ the better fit for a mid-size room, a large room and a very large room, and Rotel A12 for desk or near-field listening and a small room. Match the amplifier to the room you actually have, not the one you want. |
| Noise floor | A | Arcam A15+ is the quieter design on paper - 106dB against 100dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Analogue inputs | B | Rotel A12 takes more analogue sources - 4 against 3. |
| Room to grow | evenly matched | The same expansion options on both. |
| Price | B | Rotel A12 costs less - $800 against $1,500 at list. |
| Watts per dollar | B | Rotel A12 is the cheaper watt - about $13 per watt against $19. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Arcam A15+ B Rotel A12
depends neither is better in the abstract - it turns on your room, your system or how you will use them. Only specs published for both amplifiers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
Neither runs away with it - they trade advantages. Let the "depends" rows and the speakers you already own settle it. Think about the whole system: the roughly $700 saved by taking the cheaper one would buy better speakers or a subwoofer, which does more for the sound than the difference between two competent amplifiers.
What a spec sheet cannot show: how either sounds with your speakers, how the controls feel day to day, and what the app is like to live with - which is where most all-in-one amplifiers are actually won or lost. Power figures are the manufacturers' own and are not measured to a common standard, so treat small differences as noise. If you can hear both, that will tell you more than any row above.