How many years is a flagship component good for?

Is a fifteen year-old preamp that was king-of-the-hill in its day still a good preamp? Does a $15k preamp of fifteen years ago sound as good as a current $5k preamp?

Same questions for speakers, cables and amps.

Digital components surely don't hold up with the rapid and constant advances in digital technology.
as long as it fulfills your desires.
When it looks old to you, then it is time to replace. If you have state of the art components, then whenever your heart desires a new bit is all it takes.
IF you are asking because you want to buy some used state of the art from 'yesteryear' and wonder where to start?
THEN: you gotta read the reviews, old reviews.
Some stuff is CLASSIC. It will (within this lifetime) be reguarded as wonderful. Marantz Model 9, Audio Research Sp-10 (with great tubes only), Audio Research Reference 3, ingeneral, Conrad Johnson, Audio Research, Mark Levinson, Classe, Boulder, Oracle, VPI,
Anywy, forget DACs, Forget CD players and transports. They are gonna break down and old means NO PARTS.
Tube gear NEVER really get too old. Turntables and certain carts.. old can be good. New can be good too.
Amps, replace the caps, forever, Preamps, caaps, also forever.
Phono sections, same thing.
A lot of the old good stuff is more style and romance than 'just' the sound.
(I owned an Audio Research SP-10, I did not like it, because Ididnot want to spend the fortune on tubes it needed to shine... and sold it for cash and a SP-15, way more to my liking.)
So a little study for your choice of 'poison' and your set.
Possibly forever...

There really isn't anything new in pre amps. Don't fall for hype!
I buy my gear by purchasing top end units from the past. I am just considering bringing my speakers up to 1996 from 1983. Despite their age I have heard VERY FEW that equal my present ones. I often use a tube pre built in 1987 and SS amps from the early 90s. In fact with minor exceptions everything in my system has been discontinued and was so when I bought it. I regard it as a total myth that there has been an across the board upgrade in digital as well; in fact the opposite is true in most cases. One of my DACs is the Audio Synthesis DAX from 1992, its current rating on the HIGHFICRITIC scale is 46; a current MSB that runs about $10K is 48 and many current 2 to 4 thousand $ ones are in the 20s. The Benchmark is about 25. I use a Meridian 200 transport from the early 90s as well. GOOD components age very well, the trick is knowing the difference between good and expensive, they are not necessarily the same. Current best equipment will be better than past best equipment but the cost is usually totally disproportionate. Those who MUST have the latest and the best subsides the rest of us. But even in the latest equipment there are relative bargains to be had; I see current top equipment listed here at big savings all the time; just not as cheap as really good discontinued ones.
15 minutes, as the hi end business model call for better to be available right after you purchase it. Among my antiques is a forth year old Kenwood solid state unit that puts some of the current solid state stuff to shame. You figure.
Until the new flagship comes out - unless deemed an audio classic by desireablity of the educated masses then until it is surpassed by better technology.
odds are a 15K preamp then would be like a 25K preamp now. (both are way too much for any preamp, imho)
I would put my $350 Accuphase C-200 up against any new pre and it's almost 40 yo
Stanwal, are you using Martin Colloms's arbitrary ratings as some sort of objective indicator of performance levels? That scale of his is a bit of a laugh, and based entirely on his subjective tastes. It can't be taken seriously.

Statements to the effect that a $15K premp is like a 10 y.o. $25K preamp are nuts; there is no scientific correlation between price and performance, or between age and performance. Forget such comparisons. Remember, good engineering costs no more than bad.

As always, if YOU like a piece, use it; your ears are arbiters. That said, old gear needs freshening if technical inspection sees performance dropoff.
I think the "$15K premp is like a 10 y.o. $25K preamp" statement is refering to inflation, not quality.
Kristian, I take it quite seriously as you would yourself if you knew more about audio. I have spend nearly 50 years in audio myself and am quite confident in my own taste but lack the time, money or energy to hear everything on the market. Therefore I have decided to place faith in reviewers whose taste resembles mine. I first encountered Martin Colloms when he was chief designed for Monitor Audio in the 70s. I bought all the ones they brought over to the Chicago CES the first year they exhibited over here and almost became the first importer. I have followed his work and writings ever since and know of no one else in audio who has had the breath of designing and reviewing experience that he has had. Is he infallible? No one is but I have always found his views helpful even when I disagreed with them and you cannot ask more of anyone. The point about price is that many of todays products have prices that have been inflated for beyond their worth. Ones almost as good are available at a fraction of the cost. The best is always expensive but yesterdays best is affordable for me and todays is not.