How long will it take me to play piano well again?

[alexying]

I played piano from when I was 3 until I was 11.  Probably the hardest thing I played was Beethoven's Pathetique Sonata (No. Movement 3 in 4th grade although later I learned the beginning part of movement 1.  I always had weak fingers and wrists, and since I could not find the motivation to do finger exercises my teacher always gave me easy (and boring) waltzes after the Pathetique.  After playing for so long throughout my childhood I was tired of playing piano and since I started playing viola in school I quit piano lessons to take viola lessons.  I thought it would be a temporary break at the time. 
That was four years ago, now I'm a 15 year old sophomore and I really miss playing piano.  After becoming proficient at viola and playing in local youth/county orchestras I know so much more about classical music and music theory, and I really want to go back to piano.  Playing both piano and viola is not an option because of my family's financial situation, and also a lack of time and focus.  (So please don't suggest it.) 
I really want to excel at piano again, I only want to play piano.   There are so many genre options and although it is not very mobile I'd certainly say it's more versatile and enjoyable to listen to than the viola.  I want to drop viola for piano in my senior year of high school or at the end of my junior year after my viola All-State Audition. 
My ultimate goal is the scholarship competition and solo competition for seniors at my local youth orchestra at the end of that year.  They award money to the best playing seniors  in the orchestra, and they also allow seniors to have a solo at the last concert of the year.  If I could play well enough to win money there I would be satisfied.  The orchestra in general is not very competitive but the seniors who win money at the end of the year have to be very good at their instruments, on the level that they could apply for music school. 
If I really want to and I spend an hour every day (or maybe more) practicing, how good can I get in a year?  My ultimate goal is Tchaikovsky Piano Concerto No. 1, I've been hearing it in the car ever since I was little. 

[yohankwon]

Stick to viola. You've had many more accomplishments in that field than piano. Also, you can practice viola anywhere you want, unlike piano...where there is only one place and another and you can't carry a piano. xD There are many pianists so the competition level is way higher than viola.

Also, it is IMPOSSIBLE to learn the tchaikovsky in one year after not playing for 4 years, especially the fact that the most difficult piece you have ever done is the pathetique sonata, which is easy as pie compared to the concerto.

[quantum]

Playing both piano and viola is not an option because of my family's financial situation, and also a lack of time and focus. 

You may not have the budget to pay for both piano and viola lessons, but you do not need to take lessons in order to play an instrument.  I'm going to suggest to you what you don't want to hear: play both piano and viola.  As they are contrasting instruments, knowledge of either will compliment the other.  If you already own a viola, why stop playing it?  It doesn't cost anything just to play for your enjoyment. 

It seems that you already have established accomplishments on viola.  You can use that as a stepping stool to get into piano studies. 

[theholygideons]

Go with what your gut instinct tells you. If piano is your calling, then stick to it. Playing both piano and viola is not only financially taxing, but you won't have the time to play both. Why not try learn some conducting instead of viola, in which case you won't require spending time on the technical issues, instead focusing on the purely musical side. 

Also, it is IMPOSSIBLE to learn the tchaikovsky in one year after not playing for 4 years, especially the fact that the most difficult piece you have ever done is the pathetique sonata, which is easy as pie compared to the concerto.

I disagree. If you find a mentor who has already played tchaikovsky before, than I would say 1 year is more than enough, except that musically it may appear raw at first. Also, technique comes back naturally with the correct practise regime.

[yohankwon]

I disagree. If you find a mentor who has already played tchaikovsky before, than I would say 1 year is more than enough, except that musically it may appear raw at first. Also, technique comes back naturally with the correct practise regime.

idk...don't you see a huge gap of difficulty between the pathetique sonata and the tchaikovsky? If not then, alright.

[theholygideons]

idk...don't you see a huge gap of difficulty between the pathetique sonata and the tchaikovsky? If not then, alright.

difficult is relative. You are comparing an early Beethoven piano sonata with a Romantic concerto. I wouldn't say that tchaikovsky is necessarily more difficult (excluding its length), just that they require different technique. For me, I would be glad to take up arpeggios and octaves, rather than torture my left hand with those tremolos.