Bikeracer123

I currently have a race age of 14 but by next season I will be 15. their is one race I am targeting a good finish at but the only problem is that going from 14 to 15 the distance goes from 15 miles to 56 miles and just don't know how I will even complete it. I currently am able to a 56 mile ride with a group at an 18-20 mph pace but aren't the paces quite a bit higher? Tips on training for it please. Also I do not have the money for a power meter so that is a bit of a disadvantage.

Doge

As a junior, you will just get stronger each year as you age. The normal adult training formula may not be best for you. Also - some things cannot be helped in developing teens. Some kids will be faster, some will get slower - no mater what. National Champ at age 14 likely is not at age 18 and visa versa. So enjoy it, but not everything is controllable - especially in teens.

Here would be my priority:
1 Sleep - try to get 10 hours/day.
2 Miles - just do longer rides 2-3 days a week
3 Eating. I have no proof this makes a difference, but I have seen the kids with controlled eating are also the more focused and faster ones - usually.
4 I would add, if you can, race more without major goals, just to get used to it and settle the nerves. Make it a regular thing.

After that there are things a coach might have you do, but as I have been around a number of junior racers for a few years, those are what I saw made the biggest difference.

Homebrew01

Perhaps do some 40-50 mile solo rides, and work in some intervals, such as 1-3 minutes hard, simulating when the pace picks up and you trying to stay with the lead group.

Read through this:
https://www.bikeforums.net/33-road-bi...cipe-book.html

Power meter is not crucial. Main thing is willingness to suffer, train hard, rest hard, learn.
At some point, maybe a nice used power meter will cross your path for a good price, but that's secondary.

Edit your location to include a city, and maybe someone near you will have tips about riding groups etc...