Buying an existing prefabricated house - is depreciation possible?

If it is the one with 160!sqm and basement on a 6xy sqm plot with the many gables and balconies: apparently a low price, without having calculated the plot. That is at least the outward impression: very elaborate! One would no longer build it like that today because the price would be too high.
In brief, regards

Don't get hung up on the 15 years. That is effectively still a new build. No price reduction whatsoever because of this age.

Now, aside from the market situation, in my opinion an age of 15 years naturally justifies a price reduction. The usual (calculated) useful life of many equipment items (heating, windows, ...) is already considerably advanced. If you want to maintain the value (of the building), maintenance investments will sooner or later be necessary.

Viewed differently: Buildings are typically depreciated linearly at 2% (useful life 50 years), so after 15 years 30% of the value is gone.

To avoid misunderstandings: This refers only to the building, the land can of course increase in value, even significantly more.

a 15-year-old prefabricated house from the company Bien-Zenker, which has been very extensively renovated by an architect.

what should one imagine under this "extensively renovated by an architect"?

It probably also makes sense to involve an expert.

I also think that is wise. Apart from the fact that the market currently considers different prices appropriate than the expert assessing the substance.

I am afraid that when we have to sell the house again, the depreciation will simply be too great.

When and how the real estate bubble bursts is unknown. The bank must cooperate, meaning it is not insignificant how far the banker also considers your question

Are my concerns justified or do I still have the "old" way of thinking from earlier that prefabricated houses are simply junk.

or whether he still carries this inferior image in his bones. In fact, prefabricated houses were built equivalently during the period in question; a few years earlier they were even ahead of their conventionally built contemporaries in terms of energy efficiency (although partly at the cost of later discredited "ingredients" as pollutants – however, that was already resolved after 2000).

The fact about the real estate market is that in 2016 we sold a [REH] from 1999 at the original 1999 purchase price, within the family, on the open market more might have been possible. With [Mitberster Heizung]. First kitchen. First toilets, etc. Karsten

Often, prefabricated houses are estimated to have a service life of 60-80 years, and solid houses 80-100 years. Of course, during that time, renovations or even renovations must be done more often, and in times of ever-increasing land prices, it may be more likely in the future to demolish and rebuild rather than carry out extensive renovations. Nevertheless, prefabricated houses are still classified as inferior in building insurance, for example, with otherwise identical factors, and the insurance premium is still somewhat higher. In addition, in my opinion, too much attention is paid to energy aspects, whereas depending on the type of construction, there are more important positive or negative points. Building a house today quickly costs around €500,000, and then it is considered whether I have to spend 10 euros more or less per month on heating??? Honestly, I have no understanding for that at all. It seems to have become a real sport to be certified with the lowest possible consumption, which often has nothing to do with reality.

I am completely overwhelmed by so many responses. Thank you! On the way home, I already thought that my "fear post" did not include all the facts. It is also price-determining what else is included. So as a supplement - yes, it is the house with 160 sqm and 654 m2 land - it includes a solidly built basement and the interior fittings were carried out by local craftsmen. The house was redesigned by an architect because the owner did not like the standard houses. Comparatively, the plot would currently cost about 100,000.00 euros. There is no garage, but a double carport. The outdoor facilities were built elaborately. Hope I haven’t forgotten any information now. Oh yes, worth mentioning, apart from painting, we don’t have to do anything at the moment.