iPad taking a lot of time to charge

If your iPad has a USB-C connector, it will optimally charge when charged using a USB-C Power Adapter rated at 20-30W. Most iPad models with a Lightning port require a Power Adapter capable of 12W (i.e. 2.4A @5V) or greater to charge.

5W Power Adapters (1.0A @5V) intended for older models of iPhone are inadequate to charge an iPad; if the iPad charges at all, charging will be very slow. Some third-party USB-C power adapters (and portable PowerBanks) may not support USB PD (Power Delivery). Power Delivery mutually negotiates the charging voltage; the source, load and cable are all elements involved in the negotiation protocol. Unless the Power Adapter explicitly supports USB PD, it will almost certainly fail to charge the iPad; proprietary charging standards, such as QC (Quick Charge), are not supported.

Many computer USB ports also cannot source sufficient power to charge an iPad. Unless explicitly designed for charging connected devices, computer USB ports are typically limited to 0.5-1A @5V (i.e., 2.5-5.0W).

If you experience difficulties when using an appropriate Power Adapter of 12W or greater, you might be best advised to seek assistance directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively, you can initiate and manage your support cases from Apple devices using the excellent Apple Support App. If not already installed, the App can be downloaded from the App Store:

https://apps.apple.com/app/apple-support/id1130498044

You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad, Power Adapter and cable(s) - and you can explore your available options:

Genius Bar Reservation and Apple Support Options - Apple

That is perfectly normal. That’s especially true if you’re charging starting at a low level going to a high level of charge.

Which iPad?

What charging wattage?