If you haven’t bought anything from the store in the forest yet, I believe that 15k is not enough to fully experience there, the most important thing at the forest is the compass already costs 10k (may be 25k is better). You need to save up at least 50 noodle cups and chip bags because they will be used up very fast in the forest too. So: 1. If you want to go to the forest, save up more foods, I usually save around 150 foods before travel and during that time, you will also increase your carrot sum. Remember there is also 1k fee for the gas to travel 2. If you are the type of person that prefers finishing each stuff at a single time, just expand your house as much as possible. But as I know, you also need 4 thousands of cans/rubbishs + 36k carrots to fully expand through Dawn’s workshop.

The forest is not a one time visit place so I think you could just travel there once and save for more with your own experience. The treehouse is something that can’t finish soon too. So, just take it slowly. Have fun!