You might have trouble complaining about text delay times to be honest, there's nothing in your contract with Orange that says that text have to arrive promptly.
This allows the networks to conserve resources because they can use Packet switching to send text messages instead of Circuit Switching.
As long as they're getting there eventually, there's not much you can do. (Although in my experience, ringing Orange regularly to nag them can work well for fixing issues)
I topped up £30 pound last month and got "unlimited" texts (which equals 10,000. Didnt top up this month, so wasn't expected to get any, but checked my text allowance anway.. said I had 12,000 texts and so far, they havent gone