Hello,
Here are some comments. I hope they make sense (if not a stronger player will surely correct me)
1. Answering the approach is fine too, I guess.
2. C15 seems better but it doesn't "kill" everything. Black cuts at C15 and takes a stone. Connecting at D16 instead of playing D18 seems to give a nice result for white.
3. White has made a nice wall so maybe approaching at 14 wasn't the best place. Playing around k17 might have been better.
After 15, maybe pressing down at P16 would have been good.

may end up being too close to the other black stones to be really efficient.

is terrible and gives black a very nice result because his corner is now very strong while white's group is baseless. The shape is to play at 21 (same for

).
4. I don't think there's anything to punish here. Black could not cut because of the geta, so peeping seems ok (especially since it removes white's potential eyes).

There's is a ko if played at B19.

without stones around C3 and C10, this looks dangerous. Black can shut white in by playing imediately at E5. White's two stones can live but black will become very strong on the outside and build the bottom by attacking P3. I think

would be better at E5.
At this point, if we look at white's stones, none of them are working together or doing anything really interesting.
Top left corner: this wall does not seem to have much potential for building a moyo or attacking a weak black group. Moreover, it could even become a target if black gets a few more moves in the area.
Bottom left corner: after 34, the two stones will be sealed in the corner and won't contribute to the rest of the game. They are not making that much points either.
Upper right corner: the S15 group is baseless and can be attacked at any moment by black.
So, while white could have improved the result by playing better moves locally (8, 20, 28, 34), it seems having a plan for your stones would also have helped (how to make use of the D18 wall for instance).