Although I already have the btr5, I got the btr15 because it is one of the few on the market that has battery pass-through. This means I have it permanently connected to my laptop and it draws power from the USB port instead of its battery. So I just unplug it and it draws power from the battery again.

For me, as I wanted it for travel, this is an amazing feature because I can simply have my headphones on it and I can either listen to Spotify on my phone or take calls on the computer without draining its battery all the time.

The quality and sound are classic Fiio.

I will keep the btr5 as it can be connected simultaneously via Bluetooth and USB. The btr15 has a selection switch on it. You cannot have both connected at the same time. So if this is important to you, then get the btr5

Once again, Fiio pleasantly surprises with this particular DAC, considering the price it costs. Its build quality is classic Fiio, beautiful, sturdy, and well-made. However, its sound is unexpectedly good. With a frequency range of 7Hz-40,000Hz, it produces sub-bass that vibrates the ears and high frequencies that provide the slightest details, without ever piercing the ears. It is flat, without any "colored" frequencies, with punchy bass, impressively clear mids, and crystalline details in the highs. Even in low-quality MP3s that would otherwise produce shrill, irritating highs, it manages to smooth them out. The icing on the cake is the wide soundstage it produces, with impressive imaging that makes it addictive to listen to music of all genres, as well as unique for gaming. A hidden ace up its sleeve is the balanced connector. All of this, with the ability to be used with Bluetooth connection, in addition to USB, and the application from the Play Store, where additional improvement settings can be made. However, wired connection always ensures better sound quality on all devices, but in this particular case, it is equally ENJOYABLE.