Have 1.5.5.1 version. Would like to try 2.0.X.X version

I have a website that runs on 1.5.5.1 opencart version. Some time ago I created a web for my brother which is on 2.0 version. Really like it. Would like to try updating my 1.5.5.1 version to 2.0. Can I just install 2.0 version in seperate folder on my current domain and build new web there and still keep the current web with 1.5.5.1 version? I just don't want to loose the current one if I don't like 2.0

no problem, you could add multiple Shops and Versions to a site, each one it it's own subdirectory.
Just make sure, to create an individual DB for each of of the Shops.
Ernie

Great. Thank You.

One more question. How do I migrate the database from 1.5.5.1 to 2.3.0.0 later one when I'm ready? I would like to keep all the reviews from current site.

In the marketplace search engine, type "opencart upgrade", some developers offer that kind of service.