Both of your goals - the ride and the weight - are very reasonable.

You say you are doing 30 mile rides but don't say how many times a week you are riding. If you are doing three or four rides a week, just add a few more miles each week to one ride. Do this consistently and you'll easily be doing 63 in December. The only other part is that as you are doubling your mileage you will want to be sure that you drink enough water and eat enough food during the extended rides. Do some searches both in the T&N forum and and also the Long Distance forum for more detailed information and training plans. While the Long Distance forum posters may be looking to ride 100 or more miles in a day, the same ideas on training will apply to you.

As for losing 15 lbs in about 5 months, that's only three pounds a month. Just keep up the riding and make sure you eat less than you burn. There are a number of on line tools that can help you do that (I use www.fitday.com). The simple math is that 3500 calories = 1 pound. So for each week that you burn 3500 calories more than you take in, you will lose 1 pound. I dropped 30 lbs in just under 6 months last year doing that. The first couple of weeks were a bit up and down as I was figuring out my diet, but once I got it figured out it was actually quite easy. More of a mental challenge ("NO! You CANNOT eat those oatmeal cookies in the breakroom!") than a physical challenge.