What is the price of my iPad 128 GB 2015 with accessories?

Apple will accept trade-in for qualifying devices - but not for accessories. You can obtain an online estimate for device trade-in here:

Apple Trade In - Apple

Each device is assessed its own right. If using the online trade-in, you will be sent a shipping kit for each device. Devices are returned, assessed and a credit value assigned. The trade-in value is returned to you by way of an Apple gift card for each device - and these can be used to purchase whatever you wish with Apple.

You can also trade-in either in-store at a physical Apple Store - although assessed trade-in values may differ.

Genius Bar Reservation and Apple Support Options - Apple

If your device is in good condition, you may achieve a much better financial return if you sell privately - in particular if you are including accessories with the device. If you do sell privately, ensure that it is properly prepared:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

patriciafromwausau Said:

"What would a 2015 Model #A1652 12.9 inch 128 GB iPad Pro be worth with a screen protector, keypad, apply pencil and a new charger?"

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iPad Pro Trade In Value:

Find Out the Estimation here: Apple Traide In - Apple. Up to $445, according to the site.