remove old photoshop yes or no?

Definitely,

Well, it depends but you will not be able to flow yourself with the new updated.

It also depends on the circumstances too. If you need a design fast, you can always use the one on which you have your hand set.

I made designs of 2 sites in different circumstances.

ecomse was one i designed within 3 hours (excluding html part). It is a static one.

Freshpud i tried to do it but couldn't complete it in 7-8 hours (the homepage). It was the latest version.

It is good to have it if you get some quick orders otherwise let them go.

You can, but unless you need the space, a backup install of Photoshop is always a good idea.

If your CC 2017 install hits a snag and won't open and you have work that needs to be done, you'll be glad you did.

I forget the number of times people have come in here asking how they can get back a previous version.

So at least hang on to 2015.5

I'd wait a bit and make absolutely sure that all works as you need it to before uninstalling an old version.

If you are happy with PS2017 then there is no need to have old versions on your machine unless there are some plugins that are not yet compatible with 2017.

Good luck.