I'm not aware of an Opteka 15mm macro...
Is it possible you mean the Venus Optics Laowa 15mm f/4 Macro?
With such a short focal length, you can end up right on top of a subject at high magnifications... but it has greater depth of field than you'd normally see with a macro lens. The image below is a close-up I did with a non-macro 20mm lens and a macro extension tube. Normally, with a longer focal length macro lens, the flowers in the background would be unrecognizable blurs of color. But the greater natural depth of field natural to a wide angle focal length rendered them as you see here... HOWEVER, the closest petal of the main flower subject was
touching the front element of the lens!
In addition, the Laowa 15mm f/4 lens has a shift function, which can be useful if shooting architecture at non-macro distances or for perspective corrections with smaller subjects.
Search for "15mm Laowa review"... I found several online, including some illustrated with a number of sample images made with the lens and showing what it's capable of doing.
Regarding Opteka... I don't think they actually make anything. Like Kodak, Vivitar, Polaroid and some other "brands", they simply outsource items such as lenses. Sometime rebranded products are poor quality. Other times they are good or even excellent (Vivitar Series 1 lenses and others outsourced from Kiron, for example).
I recently bought a Meike 12mm f/2.8 lens (not a macro)... Yet another "brand" that likely doesn't actually make anything. The exact same lens sells under the Opteka brand. I have no idea who actually makes it... I didn't have very high expectations. But, for $125 (demo unit) I was very pleasantly surprised at the lens' all-metal build quality and excellent feel, good fitting and effective lens hood and even with it's quite good image quality. (I posted a recent test shot done with it here
https://www.uglyhedgehog.com/t-649134-1.html#11268103. Perfect... no. Very good and usable.... heck yeah!)
My point being, don't be too quick to dismiss weird third party brands. Sometimes there are hidden gems! I'd never heard of Venus Optics Laowa brand until a few years ago... but they offer some interesting and unusual items... things you won't find from any other manufacturers. (That makes me pretty sure Venus Optics is making their own stuff.)