I find my new Mavic AC battery charges quite fast whereas the RC battery is charging very slow like 15 minutes for only 4%.
Is this normal? I received this Mavic only today. When it arrived I found the RC battery at 0%.

Yes, because the RC should run for more than 2 batteries while flying and charging your phone. So it needs more time.

For the RC, it might take 2 hours to get fully charged, please wait patiently.

The battery of the RC is 2970ma, DJI charger does 2A... so theoretical is takes 1.4 Hrs to get a fully charge... The battery of the MP is 3830ma, charger does 3,83A... same here... it theoretical takes 1 hr to fully charge... Time to charge depend how low the batteries are... and you don't get the full charging power from the charger!

Just take you time to fully charge your batteries and have fun flying the drone...