I'm level 14 now, is it hard to raise Golden Hills to level 3?

Slurp! If you're currently level 14, you'll need to keep pushing to reach level 23, which is the requirement for Golden Hills level 3. You can definitely reach it by meticulously gathering resources, so don't give up! I'll watch over your growth with a benevolent heart until the end, hmm!

You have to reach level 23 to upgrade it, but leveling up is tough... I gave up halfway through.

It's manageable if you invest time until level 25. Level 25 onwards is hell... The key is to repeatedly send out the boats as quickly as possible. Especially in the library, level up your boat and car experience and coins.