I will pay 5-6 euro for this model, if I really need this exact model. 15 euro, in my opinion is too much.
I'm able to model it my myself, but it will take; I don't know, 1 hour of my time
15 euro, maybe, for a very complex object, like bed, sofa, car and I havn't time to do it by myself.
Of course, it must be good modeled. Triangle topology in the 2018??? DeEspona ^__^ ? Maybe some bad export from .iges file?
I bought a lot from 3DSky and the price for each model is $6. They have a real Italian brand objects (Lumina, Moroso, Artemide, Fontana Arte), impossible to find in other stores.
Shaders aren't so important for me. Good textures and cleaver UVW mapping is enough.
If your price is not so expensive, you will have more change to sell it more and more times. Also it's good as "advertising" for you.
So, in the future, more people will by from your store.