DxOmark (Click here) tested the Tamron 15-30mm SP lens. They used the F-mount version on the D810 which uses the same A7r sensor. The A-mount lens can be ordered at BHphoto (Click here) and at Adorama (Click here). So how good is the lens? DxO writes:

All lenses are a compromise, but the Tamron has a good balance, with high central sharpness wide-open and sharpness improving across the frame on stopping down, and with generally good control of chromatic aberration. On the downside, it has some slight field curvature at 30mm and it has quite high levels of both barrel and pincushion distortion that are more noticeable than the Nikkor equivalents.
However, at least the Tamron doesn’t exhibit complex distortion, so it should be relatively easy to correct with software. In physical terms, the lens is large and heavy and doesn’t cover the popular 35mm focal length, but as a 24-47mm equivalent on an APS-C-format DSLR, it remains a versatile offering. Combined with its good performance and the lure of built-in stabilization, at around $1,200 it looks very tempting.

DxOmark (Click here) also tested the Sony DT 16-50mm F2.8 SSM lens:

Although the Sony has good center sharpness throughout much of the range, the exception is at 50mm, where field curvature can be problematic and stopping down doesn’t help. It also has quite noticeable chromatic aberration at the edges of the frame at 16mm and when stopped-down mid-range (24-35mm), making it look like a somewhat problematic lens. On balance, however, after taking the high speed aperture, stabilization, sonic type motor and price into account, it remains an attractive option for Sony users. But if brand loyalty isn’t a concern, potential buyers could look at the offerings from Sigma or Tamron.