I have a Yamaha C3 and have found the exact same thing to be an issue. I had tested the keys with coins a while ago and found a similar weighting ~64g @ A4. It's frustratingly heavy for my tiny hands/frail little arms.
Since you own the C3 you might want to contact a tech and get an estimate on having the keys counter weighted to a weight you would like. It's a shame to have a beautiful instrument like that and not realize the full joy of ownership.
on my AG N3 you can ajust the weightof the keys touch, in the control panel by tapping in either 1 2 3 accordingly from light to heavy hope this helps