At 15 weeks old he is going to pee every 5 mins.
It's what they do and it will get better. One tip is to stay outside until he goes a few times, making sure he is truly empty when he comes back in.
If at all possible, you need to pick one method and stick to it. Pads or outside only. It's much harder to change later. Do a search for "Crate Training" on this site and you should find some valuable information. Let us know what you decide, that will make it easier to help.
As far as the barking, you have to ignore it. If barking gets him attention he will do it more. This is also where a crate can help.
Loki is totally outside trained, so I promise it is possible. It's a lot of work at first, but so worth it.