Thanks to all for the comments and suggestions. I try to learn with them.
I was read that it was soft wide open, and because of that I shot in f2 and up.
(To Carlwashere: Yes, I shot all static objects)
Here are some samples with the 50 mm and the 15-85 mm. Non post processing except flower 15-85 that has Lightroom Vibrance.
I know it's not a fear comparison, because are different objects, settings, ambient light, etc.
I'm just talking about the impression I have when I see one or other picture.
The first two was taken with the 50 mm. The first one looks fine, but I don't know, still not sharp like some pics with the 15-85. The second one looks out of focus or not sharp, what is it?
50 mm, f/4, 1/400, ISO 200 - Mode: Program
50 mm, f/3.5, 1/320, ISO 200 - Mode: Program
Now two with 15-85 mm, I can't believe how sharp they're.
15-85 mm, f8,1/200, ISO 200 - Mode: Program
15-85 mm, f/10, 1/200, ISO 200 - Mode: Program
Canon EOS Rebel t6i | Canon 15-85mm IS USM | Canon 50mm 1.4 USM | Canon 70-200mm f/4L USM