Single front tooth veneer. Will it still match my teeth in 15 years' time?

Your question is one that comes up all the time, and the answers from my dental colleagues are all correct. I write to add this one additional point. 
Teeth are made of two very different materials (enamel and dentine) layered one on top of the other. Added to this structure are the food stains and structural loads of life. Whitening teeth corrects the staining part, but the other physical changes still go a long way to make tooth look unique - they will chip, crack and wear. 
Porcelain, of all the different types can be made to look very similar to natural teeth in some circumstances but cannot recreate that everywhere under all lighting conditions. From indoor fluorescent lighting to daylight/overcast/night lighting/stadium/museum/restaurant - the list is endless. There will always be times when the 'perfectly' matched tooth will look slightly wrong or fake over the course of your week even when the veneer is first fitted. This is why many dentists insist on either 2, 4 or 6 are the minimum number. 
My aim is to always make clients look natural so I have to be honest that an artificial material will struggle depending on how demanding the client is. 
Having said that, ending at a strong delineating point is a good idea. Your front two incisors have their own space, but that space is strongly influenced by the two teeth either side (the laterals). Stopping at the front four can be a safe compromise as the canines look so different in shape/colour/texture that changes over time will be less obvious to most of the people you meet and to yourself I believe.
Conversely - if you do only have one veneer done and you have to change it in 15 years, you will have spent less on the treatment in total and affected/removed less tooth structure in total - as long as you understand the limitations of what that means. 
Hope that this helps you to decide
Kind regards 
Thomas Dey BDS, MSc

Hi:This is a great but difficult question to answer.  The main worry is the staining of your own natural teeth in the next 15 years that can cause the mismatch.Best,Dr. Maddahi

The enamel on our teeth undergoes a constant evolution thru our lives.  As we age, our teeth generally get darker in color. Even if you don't drink coffee, tea, wine, or eat anything with color, your teeth will stain over time. Taking this into consideration, I generally recommend that you place two veneers, one on each front tooth. This will give you better longterm results than a single veneer. Even though your teeth may discolor over time, having two front teeth that match in color looks much better! You can always whiten your other teeth if they start discoloring and become darker than your front teeth.