Will Siri get faster?

I believe it depends on your network speed at the time, not the capabilities of "Siri" itself. Better cell reception and speeds will mean faster Siri response time.

Yes, Siri learns and will improve both in speed and in correctly recognizing what you ask as long as you don't turn Siri off (in the Settings) which deletes the caches from Apple's servers. From the Siri FAQ:

Does Siri work out of the box, or do I have to teach it?

Siri works right out of the box, without any work on your part. And the more you use Siri, the better it will understand you. It does this by learning about your accent and other characteristics of your voice. Siri uses voice recognition algorithms to categorize your voice into one of the dialects or accents it understands. As more people use Siri and it’s exposed to more variations of a language, its overall recognition of dialects and accents will continue to improve, and Siri will work even better.

Siri also uses information from your contacts, music library, calendars, and reminders to better understand what you say. So it responds more accurately when you ask to make a phone call, play music, or create an appointment or reminder.

If you like, you can reset what Siri has learned about your voice by turning Siri off and then back on in Settings > General > Siri.

Regards.

Apple's servers do all the processing of voice recognition - to the best of my knowledge, none at all is performed on the iPhone itself - so network connection spped will always been involved. That's why Siri doesn't work in absence of an Internet connection. Only if voice recognization was processed on the iPhone itself would instant response be possible, and that's not likely to happen anytime in the near future; it would just require more processing power that the iPhone has, or at least can spare from other functions.

Regards.