Engine has had complete rebuild 15,000km ago. Fuel consumption was 24L/100km (10MPG) Replaced injectors and fuel consumption is now 38L/100km (6.2MPG) Ignition system is new and fuel system is new.
Trouble shooting 101
When you have a new problem after works been done, go back and recheck everything that's been done.
Be suspicious of everything new
1st in your list is engine rebuild.
24L/100km is too much for a fresh engine.
Even if you make the assumption a fresh engine is gonna be tight and use more fuel until it's run in, I wouldn't expect it to use 30% more than what's typical. And by 1500km, it should be running free and easy.
What was your run in procedure?
Had anyone verified the critical mechanical stuff is correct?
See my list above?
Why new injectors?
Were the originals flow tested? Inspected?
How many km in the original injectors?
I've made inquiry's about having injectors cleaned at 250k km, and feedback from more than one supplier has been not to mess with them. Toyota injectiors rarely need cleaning.
Be specific about what's new in the ignition system and fuel system?
New doesn't always mean good. Aftermarket parts can be problematic. OEM Toyota parts can be no good fresh out of the box (not common, not unheard of)
There's loads of people on this forum w with more knowledge than me
The more detailed info you share, the more likely someone is to be able to help.