I don't know what the second hand car market is like where you live, but just in case it's similar to the UK, it's possible to get a second hand hybrid electric car for similar money in the UK. For example, can get a second hand Prius for less than £3k if you shop around:
http://m.ebay.co.uk/sch/i.html?_sacat=18290&_from=R40&_trksi...
I'm not sure that's a fair comparison though. a Nissan LEAF or Renault Zoe will probably end up around your 4k euro price when they get to be 7 years old too.
My point is that if you want an affordable EV option, they exist. You don't have to be an engineer to afford an electric car anymore, they've become reasonably cheap, and prices seem to slowly be dropping every year
What? Where? Denmark? I'd seriously consider. Here (Finland) they are completely unavailable as used, and new ones start at 32 990 €.
It looks like a new Zoe sells for exactly half the price in UK (14 k£ , 16 400 €) than here in Finland (33 k€). Is there a substantial subsidy on electric cars in UK? Here they have less tax than others.
Bear in mind that with many examples of Renault and Nissan EVs, you also have to pay a mandatory monthly battery leasing fee - even as the second or subsequent owner. So the headline purchase cost is only part of the price.
There are some Zoes, and a larger proportion of Leafs, in which the battery is owned outright but one has to check before purchasing.
Even including a brand new battery, total cost is still well below your 15K EUR max budget, using real-world numbers you can actually purchase with today :
http://www.autotrader.co.uk/car-search?make=RENAULT&model=ZO...