Going to make a somewhat lukewarm defence of the 1510. I haven't actually used it, but I have the very similar 1608 from a few years ago. Not sure if the 1608 measures as badly (it uses a slightly beefier amplifier section and I believe a different DAC, so it could be different).
I wouldn't recommend building a high-end music system around these receivers. However, if you're looking for a receiver to use in a general purpose system, or a system that's primarily for movies and gaming, they're awesome. You get tonnes of HDMI inputs, really excellent video upscaling and lots of options, built-in room correction - the works - for under $1,000. In a situation where a bit of high-end roll-off and a moderate amount of distortion aren't going to trouble you (like movies and games), it's a really solid option.
It is a shame, though, that the unit performs this badly since we've seen many cheaper options put up much better numbers and it seems like mostly laziness on the part of Marantz engineers. It's also a shame that the preamp outputs on these units are so shoddy - I ended up upgrading my 1608 to a Denon 3700h because I was switching to using a separate power amplifier and the preouts on the 1608 just would not output a respectable signal level. The 15/16/17xx series, based on their size and feature set, would make for a really fantastic preamp if they just had decent DAC performance and could output at a reasonable level from their preouts.
I think people who are saying this unit is "garbage" and a "waste of money" are kind of missing the point, and not paying attention to the typical use scenario for a receiver like this. Yes the DAC and amplifier are disappointing and should be better, but people who are buying these are generally not buying them for a high-end music system. They're buying them to plug three game systems, a bluray player, and a streaming box into it and run an inexpensive 5.1 system for movies, games, and occasional music listening. For that use case, these small Marantz units are absolutely fine.
