How to have 2 versions of iTunes? Must I upgrade?

You have to abandon the old ones because unlike your great grandmother's potato masher from 1902 which can still be used to mash potatoes today, digital technology is far more complex. Items are replaced by something new every 6 months and do not interface with the old because of vastly different capabilities. That is simply the way of the 21st century. Either that or do as I do which is not buy an iPhone, or iPod, or iPad, or use any new software, be patient with very slow web page rendering, and still use a 14 year old computer with iTunes 7.5 which is rock solid. Convince the world not to jump on new technology so fast and maybe the electronics companies of the world will change their ways. Good luck.

Only one version of iTunes can run on a computer at a time. Because you are using iOS9 you are in a bind if you want to use iTunes to sync because it requires iTunes 12.3+. I guess you could learn how to use your iPhone in a more limited manner without iTunes. With the advent of Match, Apple Music, and iTunes Store purchase re-downloads (if you buy your stuff from them) traditional syncing isn't as critical.

A library opened by a later version of iTunes can no longer be opened by an earlier version so even if you could run two iTunes you would have to have two libraries (you could share media files though).

Maybe you could implement something fancy such as running a virtualized version of Snow Leopard server inside a Mountain Lion+ environment. I think you might be able to run a separate version of iTunes that way. Either that or set up a dual boot system where you boot to one or the other as needed (a bit of a hassle). Or buy a second computer (I have 2, one with Tiger OS and the other I am setting up with Mavericks + Snow Leopard server).

It's not what you spent 5 years ago that matters, it is getting the future customer into the store. People sometimes come on here and accuse me of being a fanboy but in reality although I use Macs and provide pragmatic answers (= not always what people want to hear) to these kinds of topics I am a prime example of why it isn't the past that matters, it is next quarter's profit postings. I have been using Macs for 25 years but apart from $20 I recently spent buying a set of system discs for a 7 year old computer I have never actually bought anything directly from Apple. I have always bought used or been gifted retired machines. So in some ways I am a long-time fan but as far as a for-profit corporation is concerned I am doing nothing for their bottom line. I can hardly blame them if they are no longer writing applications for my G4. 🙂 Also remember that the percentage of users still using older machines that have reached the unsupported stage is very small compared to the number of people clamoring for the next hot item. So where will they invest their time and effort? Pay programmers to code for machines that represent a small number of the total in use and are not actually bringing in income, or pay them to develop the next thing which will get the millions standing in line to spend hundreds of dollars each?

Sure, you can edit a post for up to 15 minutes after it has been posted.

It does seem foolish that Ringtones aren't yet part of iTunes in the Cloud and available for direct download on the iPhone via your purchase history. Probably some sort of music industry licensing restriction involved.

I actually stopped connecting my iPhone to iTunes a few years ago and never sync anything over USB. I back up my phone to iCloud, update apps via the cloud, sync contacts etc. via iCloud and music and photo's all sync via the cloud. If you're able to do the same then you should be able to hold on to your older software versions on the Mac. Time eventually catches up with you though and there will be other requirements to update.

Its a costlier solution but I know many people separate their production systems from their personal Mac's. Its definitely common for production systems to lag behind with respect to OS and software versions for stability and compatibility reasons.