Is the Tamron 15-30mm f/2.8 Di VC USD G2 Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 18mm f/4.0 test image. Observe the contrast and resolution of these results.
Is the Tamron 15-30mm f/2.8 Di VC USD G2 Lens set to 18mm f/4.0 sharper than the Canon EF 16-35mm f/4L IS USM Lens set to 20mm f/4.5? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.