One is a streaming all-in-one and the other is an amplifier. Judge them on how many boxes you want and what you already own, not on the spec sheet alone.
| Area | Better | Why |
|---|
| Power | evenly matched | Effectively the same output - 80W against 80W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Grip on hard loads | B | Rotel A14 MKII holds up better into a 4-ohm load: its output nearly doubles to 150W, where the other increases strongly. That matters with demanding speakers far more than the 8-ohm figure does. |
| 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 | B | Both decode on board. Rotel A14 MKII goes higher - 384kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Streaming | evenly matched | Only Rotel A14 MKII has Roon. Neither list is longer in a way that matters - check the one service you actually pay for. |
| Analogue inputs | B | Rotel A14 MKII takes more analogue sources - 4 against 3. |
| Room to grow | evenly matched | The same expansion options on both. |
| Price | A | Arcam A15 costs less - $999 against $1,600 at list. |
| Watts per dollar | A | Arcam A15 is the cheaper watt - about $12 per watt against $20. 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 A14 MKII
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?
Rotel A14 MKII is ahead, but on only 1 of the measured areas, and it costs about 60% more. That is a lot of money for a narrow margin - Arcam A15 is the sensible buy unless a specific feature above decides it for you. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Rotel A14 MKII is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. Think about the whole system: the roughly $601 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.