It is a good idea to purchase a vintage tube pre-amp.

There are many new and used preamps in $2000~3000 range.
First, some questions; what amp are using, do you want balanced or single-ended (RCA) input/output? Do you seek a warm, "tubey" sound or more neutral and transparent?

You may not need to go back 10-15 years for used. It depends on the quality of your components you are adding to. For example, Your budget could get you a nearly new Conrad Johnson...
https://www.audiogon.com/listings/tube-conrad-johnson-et3-se-line-stage-preamplifier-2017-01-23-preamplifiers-12601-south-road-ny

or a new Atma-Sphere pre with phono stage...
http://www.atma-sphere.com/Products/#UV-1

or an amazing deal on an ARC...
https://www.audiogon.com/listings/tube-audio-research-ls-17se-immaculate-7mos-old-2017-02-12-preampl...

IMO, a 10+ year old preamp is a good value, but realize that it will need to have some internal parts replaced due to age. So add about $300 (plus tubes) to the price of an older component.

I think it certainly can be a good decision if you purchase for the right price taking into account tube replacement and replacing/upgrading parts as noted by lowrider. BTW you mention the SP15, do you require a phono stage?

For $2-3K you can get a really good used tube pre, especially if you don’t need a phono stage. But even if you do. Not to disagree w my esteemed colleagues, but most tube pre-amps (with some notable exceptions) are very easy on tubes, so I would not necessarily believe that you would have to budget for replacements. Even if you so, there are many good new stock small signal tubes available w/o breaking the bank. There are lots of good ones for sale now; in addition to the CJs and ARCs, there are models from Audio Note, BAT, and Modwright available well within your budget.

BTW, it's my opinion that a good pre is the heart of a good system, you can't go wrong here with getting the best you can afford.