I want to add two recessed lights to an existing recessed light. The existing light has 14/2 wire running from a 15amp. I have extra 12/2 wire. Can I connect new 12/2 wire to the existing 14/2 wire?
There is no prohibition to use larger wires.
But it is generally considered as poor practices when there is no specific reason for it, such as using a larger guage wire for a long run to reduce voltage drop.
Some one working on it in the future might be confused and think that the whole circuit is #12 and replace the breaker with a 20 amp one.
Also if you are making the splice in the can light box check the box fill. Those boxes are small.
But it is generally considered as poor practices when there is no specific reason for it, such as using a larger guage wire for a long run to reduce voltage drop.
Some one working on it in the future might be confused and think that the whole circuit is #12 and replace the breaker with a 20 amp one.
Also if you are making the splice in the can light box check the box fill. Those boxes are small.