Q: Improving ipad2 performance running iOS 8.4.1

How much empty space available?

One option to consider

Backup to iTunes and then restore as new which will install iOS 9.3.2 - see if a factory fresh iPad works to your expectations

Or of course you can continue using it as is

500 Mbs is NOT NEARLY enough operating space for an iPad.

If you photos you want to save, you should NOT be just willy nilly picking out which ones to delete.

You should be backing up your iPad data to a computer running iTunes, iCloud or other cloud services like DropBox or to specialty mobile devices like specialty flash drive or specialty mobile, portable hard drives for backup  before just deleting stuff off of your iDevice.

You need to recover between, at the minimum, at least 3-6 GBs of free storage space.

Consider deleting apps you haven't used in a long time before deleting actual important, personal data off of your iDevices.

MichelPM  is right as usual - do not delete any image until you have it backed up is the usual recommendation

Import photos and videos from your iPhone, iPad, or iPod touch to your computer - Apple Support